With the assumption that I know shit all about running a community and I see this as a cool side project that may or not be profitable and may or not help orange pill some non techies (I'd probably do a gardening sub or something), I'm thinking 100-200 kilosats a month but I'm sure you can get a better offer from some of the folks here.

mudbloodvonfrei

bitcoin

Technical and Programming - Tutorials and Help - Sub Suggestion

l0k18

yes to both, and so in theory if your sub was a popular one with lots of transactions and fees, you could actually earn a profit for running it