Answers

Some colleges have "rolling admissions" which means they accept people as applications come in. Other schools will consider all applications which arrive before the deadline at the same time. You have to check with the schools you're applying to.

generally selective schools do not employ rolling admissions, so if you're really worried about getting in, it probably won't help to send in your application earlier. Generally schools that receive and accept a lot of applications will use rolling admissions to smooth out the application process.

definitely apply to schools with rolling admisisons first because your chance of getting in will be higher. Each time a school accepts someone new, with rolling admissions, your chance of getting in becomes smaller and smaller.