There i lots of criteria to choose the right bounty so you won't be wasting your time:
1 - Chose only SOLID & PROMISING ICO / Projects.
2 - Do as many bounties as you can (they are profitable if you're smart enough).
As for how to get Twitter followers, it's easy, just go check those Follow & follow back FREE websites to get fans, by the time you'll be having 10's of followers so easy, yes this take time but totally worth it.
not always the number of projects affects profits. You can make 100 bounty and get a small profit. or make 10 bounty and get a pretty decent reward. it all depends on the approach