What helps the most buildings, troops, or decrees? What should I upgrading? Should I level them all evenly over time? I would appreciate some tips on what I should do
Be sure to level up everything about equally and see whatever you can and can't miss. Player level matters a lot too. Both for every 20 levels in coloseum and battle square gives a higher ranked building and troop atk and hp. That is, from 50+ from what I know of.
I think maxing decrees helps a lot.
Also max damage reduction on buildings. If you do not have this done, you will forever be frustrated as you get killed so fast.
And maxing your bastion helps in other modes as well, so it is one of my priorities.
Everything else is less important imo.