I went back from 4.5$ to 10$ but I wouldn't recommend trying that to anyone (one bad hand and you're out, I myself got lucky with some pocket aces vs QQ or KK or something ). Anyway, the more the merrier. If I were to deposit again I'd consider something along the lines of 20-30$ so you can multi table comfortably (and not get bored ). You can also multi table with like 14-16 $ so no worry, you just have to be comfortable with it. I am talking about the micros (2nl ) mind you
Anyway, good luck and take care.
Almost forgot, bankroll mob can help you with some free $, no deposit needed so maybe you can check them out (I did that recently, it takes a few days to process )