As a general rule, after May 1 you can only hold one acceptance at a time, but as many waitlist spots as you want. So yes, if you are accepted off the waitlist at one school and accept the spot, you can still remain on the waitlist at other schools. If accepted by a preferred school you simply withdraw from the previous school and accept the spot at the preferred school. And yes, it is possible that one of those schools will offer you better financial aid if accepted. However, schools are under no obligation to provide a financial aid package before the response deadline they provide you. I hope that helps.