The best way to level up your plaza is either to participate in Global Missions, such as the past GTS one that earned PLG Accounts 4k FC. You just needed to keep getting more FC, and you'll level up past 40 on that alone. Otherwise, preform regular missions, while annoying, they can earn you on avg 30 FC per run.Oh joy.
Any guides on getting plaza lvs and specific buildings? Have totally ignored it and I'm lv 3 right now. ;p
Edit: As to the glitch question,
Apparently, this. Did not know about it. However, given how TPC has been acting with bans, Imma not risk it.