For Final Invitation it's best to wait until you have the full Akantor armor. An alternative is the Rathalos Soul U armor. I found it easiest to fight him with a Great Sword, I don't know if they are still up on You Tube, but that's where I learned to fight him with a GS.
If you want to go long ranged against a Plesioth the Dragon Bow Solar is an Thunder attribute bow. If you go close ranged the True Devil Slicer is good. By the way, In case you don't know, remeber you can fish a Plesioth out of the water by using a frog when he hasn't spotted you. He takes damage from that.
The armor I used before attaining the Akantor was the Rathalos Super. It gives you Attack Up Large and Speedy Recovery by adding a few jewls.
The Onslaught Hammer is also a good weapon, I believe it's one of the best hammers. Most of the other weapons you mentioned aren't that useful.