Level first and foremost, bronze rate is higher at max level. Make sure to run daily instances and do the three Infinites dailies for the threads that greatly boost stats. Raids bosses and daily instance stuff gives mountains of bronze.
Is that the Heirloom one? If that’s all you want then all you need is a single Heroic SoO run, probably. Level and just keep applying to them in group finder once you can see them (I think maybe 45?), maxed out people can basically solo it so eventually you’ll probably catch an invite and get carried along.
I didn’t waste my bronze upgrading gear, there is no m+ in remix and when remits over your gear will be converted over hopefully 424’s the gear level is unknown at this time
I spammed LFR, dungeons and quest to level up and get my bronze. Don’t forget to do the dailies.
It can only be obtained by running SOO on normal level or higher. Normal requires 2 runs to get the bones, Heroic, requires 1 run. Mythic requires 1 run. Every run should give more than enough bronze.
To get it just go to premade groups, look for a run and apply. You have to be level 60 or higher. Spamming heroic dungeons and scenarios should get you to max level in a day or two. Some people do it in three hours. Throw in some raid runs and get the experience threads and you’ll get there faster.
Whenever it will let you, honestly. You have to hit a certain level for Siege to show up in groupfinder, I don’t remember off the top of my head which one.