Pay attention to what drivers are available for each OS. In particular, it can be difficult to find DOS sound drivers that work well with something that new. You can install Windows 98 and use it to boot to DOS as needed although I have personally found 98’s DOS mode configuration to be awkward to use. In these situations, I tend to use system commander to dual boot with a small DOS 6.22 partition: https://winworldpc.com/product/system-commander/2000-5x

I have found that the new adapters you can buy are very unreliable. I ended up buying a 20 y/o USB 2.0 dock on eBay and that seems to work with every drive I throw at it.

Plenty of BBSs around: https://www.telnetbbsguide.com/

Or for an old school web experience there is neocities: https://neocities.org/

I built a C64 laptop using one of these. Here it is on a train ride connecting to a BBS.