I actually use both types of screen. The steel braid is in my mash tun and the kettle screen is in (oddly enough) my kettle. I use a longer screen in a rectangular cooler but if I had a set up like that I personally would probably go for the kettle screen, it is sturdier and won't move around on you.
I already have a nice propane burner that I've used for full boil extract batches, so I think I should be ok on heat. I did realize that with a 15 gallon pot I'm going to need a larger immersion chiller.
I do need to get 1/2" tubing, currently all I have is my plastic auto-siphon.