3. Check the spreadsheet, if you think the project is good and there are fewer participants join the campaign lower participants bigger shares.
About those two points. I think you need to calculate bounty reward based on max participants allowed.
If you join in first week of bounty, you will find participants is still few.
You are right you will find few participants during the first week so it is the best time to join the campaign to build your stakes when everyone is not participating.
Because no matter how many max participants we cannot tell how many persons will going to join and finished the campaign. Joining in the early stage is a must.