Hi Claeris, welcome. i think if you just want to browse the sites you can do that once your dreampi and web browser are configured. i dont know how many sites are still operational but i know some have been brought back to life, doesnt hurt to just check them and see once your online.
heres a link to the backups if you didnt know about them https://www.dreamcastlive.net/website-backups
the fps games are much better with a mouse and keyboard so i would recommend getting a mouse with that keyboard you have on the way, but you dont need it if you dont want it. the keyboard is more important anyway if you like to chat while gaming, like in PSO. Maximum Pool is a game i would recommend if you havent considered it, seems like plenty of people like it and it is actually a fun game with lots of modes.
i love the idea of the dreamcast game night, hope you follow through with it!
if you run into problems dont be scared to ask for help in the main page chat, post in the forum or stop by the discord: https://discord.gg/ZzyQB7r