Guild Question
Who can build those depends on the permissions set for the different rank. You can also get some of those banners with guild commendations which are obtained by doing guild missions. However it is better to save commendations for ascended accessories.
You really don’t need the +xp and you should wait until 80 for the +mf. That tiny bit isn’t really going to do much.
Only guild leaders can activate/queue upgrades or ranks with special permissions. It depends on the guild and how much influence they invested in both the Economy and Politics category. For example, at Economy level 1, the guild unlocks exp/mf banners. At level 3, unlocks +10% mf for 72 hours for every guild member representing.
As mentioned above, you can get your own banners for guild commendations, but its recommended you save them for ascended/skins. I’m sure though if you want a banner, your guild leader wouldn’t mind, they dont cost that much influence anyway.