Me and my friends check the number of participants, how qualified and promising the project is and of course whats the income.
The income you cant predict. Every day new participants are joining and when it is really cool campaign you can expect that the number of participants will be huge.
Of course not, but you can always join in the middle of campaign.
You can view the evaluation of the project on reputable sites like icobench, trackico ... in addition look for reputable bounty referral channels such as bountyhive, bountyplatform ... good luck
You need to do your own research, most of these sites are not doing research, they accept project without checking team and I think ICObench is checking team members only if they have score above certain point.