Stillen cbe install question

Winn

Hi all, I will be ordering a Stillen cbe in a day or two and had a few questions.

Reading the install instructions it says it includes 3 gaskets. But it looks like 5 are used. They tell you to reuse the factory ones at the cats. Is this a non issue? I assume they would not say so if it was a problem. (if I should be
ordering 2 what am I looking for standard 2.5" exhaust gaskets?)

I will be having my local guy install as I have no way to lift the car enough.
While this guy is a good mechanic I don't think they have a lot of "exhaust"
experience, so I want to lay out the considerations. With the slip joints on this is the approach going to be try just the gaskets and the included clamps then if leaks add RED RTV in the mix or use it on all joints out of the gate?

I am thinking you don't want to use RTV unless you have to for the sake of future alignment needs etc. Not sure what the odds are of good seals on all this without. Thanks for any help..
2013 base+sport 3k mi.