hi, welcome to the Forum. OK I do my best to help --
1. yes it is possible to have more than one supervisor for our PHD, usually the PI is the one who is your main supervisor - and he is usually the one who has applied for the grant (which supports the project)
2. If I were you, I would go and look at all the scholarship websites, and look for those covering my area, see their eligibility criteria, you post this question here, it is hard for people to help you, you need to look by yourself
3. don't really understand this question -- if I am not mistaken, it's like this -- you have a research idea (or you may NOT have an idea), you either look for a scholarship offering that project OR you write to a professor and talk about what you want to do etc., then discuss, then apply, then get interview, then PASS the interview, get offer letter, then your research plan is worked on IN FULL, and you start your phd -- register at uni etc.
4. its not a bad thing, you just need to highlight what are the DIFFERENCES in your research, what more do you bring to the field, what else can you show - even though this work has been done before by his phd student.
hope this helps, and have a nice day
love satchi