Last time I asked around on 2.5G ethernet I was told to skip it and go to 10 Gigs straight as its “cheaper” and better than 2.5G. So I started to investigate and I am baffled by the costs. Let me break it down:
Quality 10G switch Mikrotik CRS305-1G-4S+IN ~150 $ (this seems reasonable)
10G SFP+ RJ45 modules - these are starting from 50$ on ebay from china which seems excessive, given i would need at least 4 of them.
10G NIC -Intel X540 T2 for around 40 $ if I want to go with RJ45. X520 with SFP+ connector can be had for 30$ but does not seem to worth it, given then price of SFP+ modules.
So I am somewhere around 430 $ for connecting my NAS and desktop PC via 10Gig. Compared to that, I can upgrade to 2.5G only for approx. 80 $
I could partially go with fiber instead of copper, pushing down the SFP+ module costs to 15$, but i still need at least one RJ45 module to run to my home PC. Also I am concerned fiber will bring some additional complexities that I am not prepared for (have zero experience with it).
I tend to see 10G SFP+ modules for under $10, LCLC fibre cables are the same for ~10m lenghts and a NIC is, as you said, around $30. So fibre is cheap, but you can also occasionally find Aquantia-based 10GBASE-T (RJ-45) NICs which can do NBASE-T (2.5G and 5G) for $35, which is a good price, considering that these are generally more efficient than the older Intel chipsets and are just as fast.
That aside, your plan sounds good, I hope it’ll work out well for you. USB3 adapters are also viable for 2.5G, so you can easily connect laptops and mini PCs that don’t necessarily have extra thunderbolt or PCIe connectivity for a 10G NIC. What I suggest you avoid is the 5G USB3-based NICs, because in reality, they can only do around 3.5G and they also run much hotter and are significantly more expensive than the 2.5G variants.