Question 1: Is viable go in "Built to Destroy" with 3 star set?
Sword(2* and 3*):Tempered Honor Blade, Brandish, Calibur, Flourish
Gun(2* and 3*):Antigua,Prismatech Alchemer Mk II, Super Blaster, Autogun
Bomb(2* and 3*):Super Blast Bomb, Freezing Vaporizer, Spine Cone
Helmet(2* and 3*):Brute Jelly Helm, Gunsliger Hat, Cobalt Helm, Wolver Cap
Armor(2* and 3*):Solid Cobalt Armor, Wolver Coat
Shield(2* and 3*):Great Defender, Great Honor Guard, Fire Break Shield
Set to Mission:
Gunsliger Hat
Solid Cobalt Armor
Super Blaster(maybe i'll upgrade to 4*)
Prismatech Alchemer Mk II
Blaze Break Shield(i'll upgrade the FBS)
Question 2:Built to Destroy is good to farm crowns?
P.S:Sorry for bad english :(
You should go fine. But for better damage, I suggest:
Elemental weapons against constructs
Shadow weapons against gremlins
You are also going to need to need someone to do well in switches. I can go with you, if you'd like. And yes, IMF is a good way to farm