Hi,

The specifications all depend on how you want to run the seedbox.
If you plan on cross-seeding multiple torrents in the swarm, then you're going to want one with a minimum of 16GB. If you just plan on manually adding torrents to ensure they meet requirements or so you don't download them on your home connection, 8GB should suffice (though honestly, for any dedicated server, 16GB is recommended).

CPU is actually quite important, as you're going to need it for hashing files. A weak one just won't do.

I'm not sure how much you're willing to spend, but I suggest regularly checking this page: https://robot.your-server.de/order/market/country/GB
Set your filters, sort by price and keep popping in to see if a server pops up (it's a sort of auction site for dedicated servers, but it's all official and whatnot) that meets your price range and requirements.