I have a relatively quiet forum on a Digital Ocean 2GB memory/50GB disk droplet and it works fine.
At the time the Discourse installation guide was recommending 1GB minimum but I upgraded at some point.
If you provide more information about how big/busy your forum is I’m sure you’ll get a more detailed answer.
I think the Discourse installer automatically sets up a swap file (I didn’t do anything manually) - so that answers part of your question, I think.