I'm not sure if this is the appropriate section, but it's close enough. I'm thinking of installing SMF on a server that is already occupied. I have 2 GB of RAM, but I only have about 400 MB to spare. I don't expect more than 30 people to use the forum, and in all likelihood, it won't receive many posts in a day.
I'd like to know, from SMF users with comparable user counts, how much RAM their forum uses on average. I haven't used Simple Machines in almost a decade, so I'm completely out of touch with what to expect.
I was running sites busier than that on a 256MB RAM VPS.
I honestly do not see any issues with the specs you list for the level of busy you have.