Young adult application and multiple GNIB ones.

Hi all,

My situation is rather confusing, hence I decided to ask for advice.
I've been in Ireland for 5 years on Stamp 4, arrived here just before being 16, got my IRP in December because it wasn't easy to get an appointment. Currently a degree student, was studying all these years, from school straight to uni. Currently have a contract which makes me a full-time worker (on paper), but de-facto they allow me to study when it is time to do so.
As Stamp 4 was achieved on a reason which is not really valid (STEP, didn't work out), I am not sure what would be the best course of action for me and what is possible.
First of all, if I will apply for citizenships, will letters from school/uni that says "this person was/is studying here from 01/09 to 31/06" all I need as proof of residence, since I'm a young adult? Do I need to write a note or explanation somewhere that I wasn't able to get my GNIB early enough because I wasn't 16? Also, if I will apply for citizenship, will that status give me the right to be here by itself?
Can I apply online to change my permission stamp? If yes, can I apply both for my current permission renewed and a change of status online?
Finally, if I will be here on Stamp 2, while having 5 years residence already, for some time before applying, will it still count as having a year of reckonable residence before the application?
If you need to clarify something - feel free to ask. Thanks in advance.