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OBS exhaust setup (thorley tri y)

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Alright I am going to be ordering these tonight just wanted to know what you guys think(redoing my whole exhaust). Also had a couple of questions. I think i already post this before but i have the cash in my hand! Plus there on sale. saving myself 40 bucks :ninja:


So my questions are:

1.) what do i need to know about installing headers? Spray it down with PB blaster? anything else?

2.) How much do you think a shop will charge to install everything back from the headers(cats/muffler/turn downs). Just want an idea before i start going to shops getting quotes.

Since the collector size is 2.50 and includes a Y pipe should i just get a single 2.50 in/out catalytic converter and run a single pipe into the muffler? or should i step it up to a 3.0 in/out cat?

or should i run it like the stock setup and run dual cats with no Y pipe?

I'm running no cats now. Really just want the most performance, make the bitch legal again, and a lot quieter - my ears are tired of ringing from long trips!