Ok for those who are wondering if it's possible to max all skills in one play or with one character, it's a yes and no. can't do it all at once as you can max about two skills per character but here's how you can get all the trophies.
First, you should be in a Free Mission character. save up ALL your xp til you get over 400,000. don't spend a single one!
(EDIT: according to this
site, to get from 18 to 99 it takes 348800 xp. )
then make sure you're in Offline mode and save your character.
then apply all the XP to one skill til it reaches 99.
make sure the trophy pops up.
reload the saved character.
apply all the XP to another skill and repeat until you get all the Pilot Skill trophies.
then do whatever you want.
It's easiest to make XP on a Zeon character (or merc but you gotta deal with the prices of MS and upgrades) so don't bother with it until you are working on a Zeon Free mission character for the Parts collection trophy.