I’d say the Cat5e cabling runs somewhere between 20m to 40m, between the switch and the closest/furthest rooms.
The last time I tested the quality of the cabling for 10G speeds, with the Fibermall module in the switch and an AQC107 NIC in a movable PC, I was able run 10G Iperf with the closest room, but connection couldn’t be established with the furthest room. Once I replaced the AQC107 NIC with a ConnectX3 + Fibermall module, 10G worked fine.
Love that thing! Great device when put into SWOS. VLAN a little bit annyoing like always with Mikrotik. But there is no fan curve. The fan only knows zero RPM or 100% which is 7000RPM. And since 30mm is a strange size, you can’t replace the fan. I had to remove the top cover and put a 80mm Noctua with a ULNA on top of it.
Not sure about that. Modern OM5 fiber cables you can really bend. I would say that if you managed to put a fat CAT6 cable through it, you would probably also have enough room to bend a modern fiber cable.
CRS304-4XG-IN
Its listed locally for about 170€, good alternative to FLEX 10G i posted if you want multigig.
General idea is
|router|<----10gbe---->|FLEX|<---10gbe-->|FLEX 2.5 GBE|
This way you have 2 nonblocking 10gbe ports available for client devices with 10gbe router uplink, or three with 1 gbe router uplink.
All your slower client devices can have 2,5gbe uplink via flex switch.
If you need more than few 10 GBASE-T, then 800€ Switch Pro XG 10 PoE - Ubiquiti Store is the cheapest thing I see.
EDIT:
This newer revision of copper sfp+ adaptor seems to be comparable to FS way up ( up to 100m and only 1,9W) and is without the extreme price tag.
The heat from longer distances using 10GBase-T is somewhat prohibitive over time (see if putting heatsinks on the sfp+).
Otherwise use single mode fiber avoiding life cycle issues & for longer distances or single mode if neither is an issue. Put a cheap switch on either side for media conversion to 10GBase-T if necessary. There are several cheap layer-2 (and layer-3) switches on Aliexpress for less than $100.
I’ve been going through a lot of the market offerings. It seems a mix of 10GbE-T and SFP+ with 2.5G and 1G ports in a L3 switch is difficult to come by.
I did find the Zyxel XS1930-12HP which has a lot of the features that would give me plenty of options, although it comes in at almost 900€ 
The ideal switch would be either
2 x 10GbE-T, 2x 10Gbit SFP+, 2 x 2.5 Gb, 6 x 1Gb. L3 VLAN routing and LACP XOR bundling support.
or
4 x 10GbE-T, 2 x 2.5 Gb, 6 x 1Gb. L3 VLAN routing and LACP XOR bundling support.
Maybe I’ve just got to wait a little longer for some more options to become available on the market.
Thanks to everyone for the suggestions. It seems the original question has been answered.
While most of the current range of switches with inbuilt 10GBase-T do support the full 100m over Cat6a/Cat7, there are some that don’t - double check with the manufacturer.
For low heat scenarios, go with SFP+ modules and be aware of the 30m/80m restrictions on some modules.
It looks like more manufacturers are bringing out products with better 10GBase-T support for those who are unable to use fibre based connections.
This switch is about to come out that is a decent price considering the number of 10gb copper ports and 400w PoE:
It has L3 capability, link aggregation, and all ports can be 1/2.5/5/10g.
Hopefully they come out with a non-poe version of the switch and drop the price a few hundred dollars.
It looks a good option and like you say, without the PoE the price point could be better. With the lower power consumption, a single psu and perhaps fanless it could come in at a more affordable cost for home users.
I’m not sure if the Ubiquiti’s support LACP XOR bundling - not all LACP switches do.
I don’t know if it does, probably not if that isnt default LACP behavior. You don’t get any options for how the LACP operates in Unifi, just enabling or disabling it on ports.