Services like Digital Ocean are great, bc. you pay as you go. So you can play with it, you pay nothing in front, no any contract.
I use it via managed service Cloudways and I m satisfied, flexible. I don’t have to care much about source … I have monitoring and if see that web eat a lot, just change higher server with few clicks.
I think there is more managed solutions which are so flexible, so it is not necessary to think so much in advance, bc. you can change source easily… I don’t mean that kind of managed WordPress hostings who put so many limitation to plugins, cache, database …
Hoe leland mentioned Digital Ocean is really amazing from my perspective, anyways with my knowledge about servers its better to use some kind of managed service. (security, performance, stability, troubleshooting)
Anyway about RAM, I run even two websites on 512mb, but its bc. these sides are not my priorities, but if I start some new project I do it on 1gb and then move up if its necessary.
Also bc. installed stack and other software its probably better to run more sites on one bigger server than every site on one small server.