Admissions process isn't selective at all...as long as your gpa is greater than 3.0 you are most likely accepted. As for sponsorship, you're going to have to take 20 credits if your gpa was above 3.2, which is quite a few classes and must be different than what you've taken in college. Some courses are only 3 credit courses so you will have to take at least 5-6 more upper-science related classes.
I'm not sure about financial aid, but each class is only about $1,200 so it's actually pretty cheap compared elsewhere.
May I ask, why are you deciding to go to HCP? You already have taken all the prereqs. Getting sponsorship is useless if your undergraduate college has a health professions office and you will be wasting another couple years (not to mention money) if you can apply right away. My suggestion is to not go through HCP or HES. Most of the students in the program are taking courses because they haven't taken the prereqs or they failed a prereq class in college and are taking it again. Sponsorship doesn't help much, as most schools do have a health professions office who can write a committee letter. Harvard HCP classes are no joke. They are pretty difficult and I would say depending on your gpa, may damage it if you don't do well.
Plus, a neuroscience major is pretty impressive already. Don't take more classes than you need. The acceptance rate for people with neuroscience degrees are much higher than biological sciences majors. If you're planning to take a year off, I would suggest something else such as work experience, travel, etc. Again, this all depends on what your situation is.