Thanks for your help guys, I just have one more question (I promise this is the last one).
To get started I was going to use 3 512mb droplets, 2 for dns servers and actually serving the websites and 1 for database querys and handling things like payments and stuff.
My last question is, how many sites realistically could 2 512mb droplets serve up ? (I don't plan on using the 512mb droplets for long, it's just while I get started, then I would gradually upgrade to 1 gb droplets, then 2gb droplets ect ...).
The reason I want to know this is because it would give me a better idea of how quickly the operating costs would go up.