The go-to at the moment for pretty much everything: https://mhn.quest/
Armor set builder standalone: https://mhnow-builder.com/
MHN Discord with sets and some guides, bug reports, local meetups, etc.
And a Niantic dev present, for whatever that’s worth: https://discord.com/invite/monsterhunternow
Most useful for me has been the upgrade calculator on mhn.quest. Shows what cross materials to save for future upgrades so you can safely clean your inventory