Feeling overwhelmed and questions about PSLF and the time buy back.

So first off I have been employed by either a K-12 or collegiate institution since 2014. I should be close to my 120 months if you include Covid and all the time with the save stuff.

That being said, I have never filled out a PSLF application, so I don't know where I am at with it. I started the process and I am overwhelmed and unsure about somethings.

1. I don't know what date I became an FTE at my first employer. What should I do for that? I was a wage payroll employee for sometime then I was made into a FTE but I am not sure when that started. Should I just take my best guess and they will certify it?
2. What time can I actually buy back?
3. I have an employer that I worked for and I not sure if they count for my PSLF? I worked for an Intermediate Unit in Pennslyvania for a few months as wage payroll after college. I have no idea what my official start and end dates are because I was an intern that started to get paid, then they just ran out of work for me.
4. Anything else I should know?