I solved that particular problem back in 2006 with an 8-port USB hub that cost me $10. Half of those accessories could probably be solved by something like this, too.
But if you really want to burn money I’m not going to stop you. Might laugh though. 
Lol, some of us prefer higher end, newer hardware. Less power drain, less chance of issues. And ive had problems with interference from hubs. It’s a poor solution for a desktop pc. Space is not an issue,so i may as well get as many ports as ill need.
Of course, you do what works for you.
I just realised that the MSI Tomahawk B450 Max is available now; that guarantees 3xxx support and got four USB 3.2 ports (one type-C, three type-A).
So, this means you pay premium for this:
So your only real reason to get the X570 is the PCIe 4.0 - if that is worth $100 then sure, else the money is better spent elsewhere. Feel free to disagree, and I shall agree to disagree. 
[edit]Oh, and I haven’t even touched on the best part - the X570 is actively cooled, the B450 is not. But, yeah…[/edit]
Pay a $100 premium for stuff to be integrated or pay $120 for a few add-on cards?
That M.2 riser won’t work/is wasted as well because the fourth PCIe slot on that motherboard is PCIe 2.0 x4 at best, which would bottleneck even one PCIe M.2 drive. It might even be PCIe 2.0 x2 because it seems to share lanes with the slots above it.
Yup B-series chipset boards also have pci-e limitations indeed.
But it kinda differs per brand how they have wired the slots and m.2’s.
Still i get what @wertigon tries to say about the Msi B450 Tomahawk,
or Msi B450 Gaming Pro carbon.
However i would personally still go for X570.
When the B550 boards come out, then it might be interesting,
to drop something like a 3600 (X) into a B550 board, and have a bang for buck setup.
I really hope that the B550 boards are going to be a bit more decent,
compared to the previous gens.
I mean they do have some price room upto like $150,- msrp now.
Although seeing Asrock’s low end X570 boards vrm situation,
doesn’t give me much faith for the rest of the B550 lineup. 
Although the both Msi boards i mention in this post, are basically the best B450 boards out there.
They have a reasonable vrm, but they still kinda use a cheap solution just like the rest.
However if you trow double the amount of ON-semi cheap mosfets in parallel on a phase,
then combined they don’t suck as bad.
But yeah i’m personally not really a fan of B-series boards all together.
Just mainly because the vrm situations on ¨most¨ of them.
And next to that the limitations of the B450 chipset and pci-e in general.
I mean yeah for a Ryzen 5 upto a 6 core i do see a good reason to go with B-series boards.
But honestly why would you limit your nice Ryzen 7 8 core, setup with a limited board?
A motherboard is still one of the most important parts of the system.
And i generally never really recommend to cheap out on one.
People would like to argue that a motherboard generally hasn’t much impact on system performance.
BUt i totally disagree on that.
Because the motherboard is actually the link between all your components.
well, i mean, looking at things, if you want better vrms, from anyone, you gotta pay over $300. but it is nice to see some amd EATX boards, even if they’re well outta my price range.
Na you can get very decent vrm’s on X570 from like the $200,- and up.
But the Asrock X570 Pro4, Mpro4 and Phantom Gaming 4 boards in particular are just terrible.
So yeah keep your hands away from those.
The Asrock X570 Steel legend is fine as far as i know.
Another very nice board in my opinion is the Gigabyte X570 Aorus Pro for like $260,-.
This board has a fully IR vrm implementation, 12+2 phase design (6 phases doubled),
and they use IR3553 40A powerstages.
This vrm is very similar to something like the Asrock X470 Taichi,
But Asrock is using 40A Ti-nexfets instead of IR3553’s.
Because the Nexfets i believe are cheaper.
Another interesting option for you in my opinion could be the Gigabyte X570 Aorus Elite.
You should kinda look at its connectivity features if it has all the stuff you need.
Because at $200,- ish it basically is a very very nice board in terms of the vrm.
Its not an IR implementation but Intersil Still you get 12+2 phases,
but then with 50A Vishay Dr-mos powerstages which are very nice as well.
eh, yeah, it’s a nice board, better vrms, but less ports and slots than the steel legend, which , to me, is the main thing steering me to asrock. asrock has a history of packing stuff into their boards
No, it’s pay $100 premium for 2/2/1 (U / S / M.2) ports integrated, or pay $120 for 7/4/4 ports? Not to mention, the riser cards could be bought as-needed, if even necessary (OP has a bunch of 1TB / 500MB drives, that could be easily consolidated into two extra 2TB SSD drives, or even a single 4TB drive).
The m.2 expansion card is a single PCIe 16x card, but there is a different problem I realize now - There would be 42 PCIe lanes required, but only 40 available (system 4x NVMe + 16x PCIe GPU + 16x PCIe NVMe + 1x USB + 1x SATA). This would be easy to solve for PCIe 4.0, since the GPU cards could drop to 8 PCIe instead…
Still, with 10 USB ports available vs 12 (4 on front of case, 6 on back), well…
You aren’t, since the 3700X isn’t saturating the B450. 
It’s adequate, but sure, some people fly first class too and think that’s a good bargain. It’s a matter of priorities.
Look at the use case. It’s buying a motherboard + CPU combo and let it sit there for at least five years without overclocking. Only upgrade will be to a better GPU in a few years time, and then I do not think it will be a $1000 GPU upgrade (for which you would need the PCIe 4.0 - rest would be backward compatible with 3.0).
If there were some chance of upgrading to a future Ryzen 4700X CPU I’d agree with you that the X570 is a better purchase. Ryzen 5700X would probably require an AM4+ or AM5 socket however, at which case the X570 will be dead-in-the-water.
you already stated a good use case for havbing pcie 4.0… if i were to go and put in an m.2 card. which probably will happen eventually
This list sofar is fairly accurate as far as i could find.
So yeah the Asrock X570 Steel legend’s vrm is fine as well.
More then fine for a 3700X.
And yeah it offers a nice feature set for the money.
Did some extra reading on lanes, and yes. You are correct, if you want to pimp out your X570 with 6 NVMe drives (and I would probably advice you to do that, actually) then go for it. It saves you all the hassle of cable managing your 3.5" drives, which is awesome.
For those uninitiated: I was under the impression B450 also allowed for 20+4+16 PCIe Lanes (20 from CPU, 4 for CPU/Chipset combo, 16 from chipset), but in 3.0 as opposed to 4.0. It doesn’t, unless an APU is involved (in which case the APU get the extra lanes). So, mea culpa! Learn new stuff every day!
Well you kinda do.
Because the pci-e lane situation on B-series boards in general.
First pci-e slot is a pci-e 3.0 x16 slot.
The second slot is sharing its lanes with m.2 etc and is gen2.
So in that regards you are already kinda limiting yourself with pci-e connectivity kinda.
But of course that highly depends on use case scenario really.
If you just run a single gpu, an m.2 and nothing else, then yeah its generally fine.
working on making it better
Ive wiki’d it so people can merge info
x470 Taichi Ultimate or x570 Taichi would be my goto picks for boards. Both should be good to put in whatever Zen 2+ 16 core+ thing AMD puts out until AM4 is EOL
Yeah, you are completely correct. That is not in any way limiting the 3700X in itself though! But I agree you are limiting yourself to single GPU + NVMe combo unfortunately, though most people won’t care about that since 3.5" drives are still plenty, or ppl have a single drive and use the cloud or NAS for primary backup these days.
Being a SFF nut myself, I’d love for a motherboard that provides 4 m.2 slots in some fashion, maybe a mini-DTX could pull it off. Heck, maybe you could have five m.2 slots on the front, one on the back, and let the GPU use the two first slots as an 8x GPU die in PCIe 4.0 fashion? That would also easily let you make the tradeoff of GPU and storage, while allowing for a single-heatsink cooler and the entire gaming PC only taking up 210x170 mm + whatever case is surrounding it… So maybe a 230x200x60 mm case running only a 140mm fan cooling everything for instance. 
I’m feeling like doing some CAD mockups here, will start a new thread for that though because this is getting way off topic. My apologies to OP.
Taichi x570 is like $350
This sounds like something ASRock would do, and throw in a raid 5 controller while they’re at it
https://www.newegg.com/p/N82E16813157883 - $300 USD atm ($330 after taxes). But I definitely understand if there’s no reason for you to go over a 3900x at stock
