Question about pci-e lanes on x370

So, as it stands now I’m currently using a system with a r5 1600 and a single 1080 TI, as well as a second NIC and TV Tuner. Very soon I will also be adding a m.2 NVME, and after that I have a series of upgrades planned. However, after taking a closer look at what i plan to do, I’m worried that this wont be possible on my current set up.
Ideally, this is what we end up with:
TV Tuner - x1 connection
Infiniband/fiber connection to NAS - x8 connection
Main GPU - x8 connection (will be passed through to VM)
Second GPU - x8 connection (to run host)
m.2 - x4 connection (will be used as scratch disk)
With this setup, both of the GPU and the m.2 drive would be run off of the cpu, no problem. The TV tuner and NIC would have to be run off of the chipset. Given that the TV Tuner isn’t really a huge bandwidth hog, would this still be an applicable set up? Or is there something im missing.
On the topic, when it comes to pci-e lanes, how are they assigned? a certain device gets a certain amount of lanes assigned at boot and that is static? or can it dynamically change? For example, if I were to be utilizing the full speed of my x8 connecting with the NIC, while not using the TV tuner, would the TV tuner simply “forfeit” lanes to the NIC?
Realistically I’d love to move to a x399 based system as I could really take advantage of a second nvme drive, maybe even in raid with the first, and the extra lanes would be useful for adding more storage over time, as I’d like to move to all m.2 ssd, even if they only function at sata speed. But, given my current budget I cant consider moving to threadripper for a good while, if at all, at least not in a meaningful way (I dont see enough benefit in just the extra lanes and platform features over something like a 1700 going to a 1900x).
Any advice or pointers would be great, just trying to get a handle on all this before I start adding in more devices.

I really don’t see a reason why your plan shouldn’t work.
You already have dedicated M.2 connection to the cpu, you can set x8 x8 sli setup…
May be you won’t get x8 for the lan, but still…
If you hold on for a bit there may be some cheaper X399 boards with 1900X, that is essentially 1800X with different core configuration.
Anyways, I really see no reason why this wouldn’t work…

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That’s what I saw as well. Realistically the x8 connection for the fiber link isn’t essential, just nice to have, since speeds would be max then. But realistically it’ll still be a huge boost over 1 gig ethernet no mater what, so I’m not too concerned

I know, and this is something I thought about. I’m already considering upgrading to a 1700, it just seems like such a waste of value to go with a cpu that costs $300 more for virtually the same performance, the only benefit being the extra lanes, which in my case is already so close to working. For that money I could build a m-itx system and put the TV tuner in there, and have a nice little htpc as well. I’d love to go threadripper and if I did it would seriously improve my performance, I just dont think it’s in the cards for now.