I am pretty sure 2.5GBe will work over normal/standard CAT5 and Cat5e cable. It’s the upstream switch that you’ll need to replace.

I personally would stick to *sense. I personally used OPNSense there’s a huge community backing, well documented, and actively maintained. I like to use the CLI, but using the Web GUI was a breeze and I mainly wanted to set it and forget it.

There are a few 5x 2.5g N100 for $120-130 USD range on AliExpress. I grabbed one a while back for my own network.