currently the fee is around 2usd for priority, there is a ICO that I want to participate in, if I pay 10usd as fee I get first in line in mined block to guarantee participation?

is there any disadvantage with having 10usd fee, maybe the transaction get cancelled?

any difference playing 2usd fee, 10usd fee, 100usd fee?
the biggest fee gets first into the mined block?