My GPA is an 84, and I want to raise it senior year before I apply to colleges, is that possible?
yes
You can raise it somewhat…but as you have already taken 3 years of classes it will be hard to get it to budge much. However, if you want to major in STEM (or humanities or whatever)…make sure you get A’s in those classes in the first and second marking periods Senior Year. They will see that you are able to do well in the harder courses in your proposed major.
I have two more classes, gym and an elective. I want to raise it to an 87 before I apply, will I be able to apply after 1 quarter of senior year?
It might be wiser to wait for RD if you want to get your grades up before applying
EA/ED would be harmful to you if you have the potential to improve your grade leading up to then