If your winrate is that 5bb/100 (which is quite good at zoom), then you need to play 24k hands to make that 300$ at NL25. If you play on every day of the month (30 days) then that would be 800 hands per day. That can be done playing just 2 zoom tables.
About picking a poker room, it depends a lot on what you are looking for. Do you want to have a lot of traffic every time you decide to play, do you want to use a hud, how good you want the software to be, do you want a lot of rakeback and so on.. Unfortunately you can't get them all. I have tried a lot of different rooms and I always go back to Stars because it is the best room for me. The rakeback totally sucks but I have to deal with it because I want to keep on using a HUD and I want to have traffic every time I sit at the tables.