Welcome Green Charizard to PN, I'm Aegis (Jito) Admin of this site.
Glad of you to join us.
Going to answer your question...
Answers:
1) Yes- As Pokeprincess n others has already explain, PN use to have a large number of members. In time from 86 members - 5 was active. And for the lack of activity in the forum - PN was shut down, Until recently it was placed back.
2) The experience levels on the forum varies from experienced members to rookies. There's a little of both casual n competitive battling, Also the members here are great individuals who will help each other, so if you need help just ask
3) The rules for becoming Gym leader and/or Elite 4 will be posted once the pokemon league is open, at the moment the league is closed - we are waiting to get a good sum of members to be able to start the league.
If you choose to be gym leader/ elite you will choose from the list of types chosen by the staff for the league.
The gyms will have a main basic rule, however the gym leaders could add rules of there own.
4) I cannot speak for everyone so you might need to individually ask, However I for one know bout EVs and IVs.
5) We the staff have already planed it, since PN started Lol
- End
I see me and yourself has some things in common I also have played since 1st gen, Also my fav pokemon is Charizard including others. I will be glad to help you out on creating new movesets and I know other members here as well.
Hope I have answered everything you wanted to know, See ya around.