You have the assembly down. I doubt that the exhaust in that link will ever add 15 rwhp.
it's true dual which means you need and X or H pipe to hook it up to the cats (catylitic converters) and up to the headers.
This is nice for engines producing a good amount pressure in the engine, something our stock v6's dont do too well.
It will let you engine breath better dual exhaus so it lessens stress, all good. but you might loose too much backpressure with true dual and lose power. I did true dual with an H pipe, and switching gears seemed effort less which was nice but I do think it took away from the response of the engine like it could breath too much.
You do not need to replace your headers unless you are looking for like 300 + hp out of the engine, the stock ones are fine
keep the cats on
Dual exhaust on a v6 looks good more than helps performance for the most part.
so it depends on what you plan on doing to the engine to upgrade the exhaust.
Say you super chrage it, then true dual with H or X pipe is that way to go.
Say just stock engine, maybe Under drive pullies or CAI, then go with a sing to dual exhaust kit, it will keep back pressure let the engine breathe and keep power and might even gain a bit
So what you really can do Is buy one of these kits, if it says bolt on, to stock bolts then yes you can do this in the comfort of your own driveway. might have to weld hangers in though :\ in any case just get a nice kit bring it to a shop and have them put it in.
It usually hooks up or welds on after the cats so the cats need no modifying or the headers, the mufflers come with a kit or you can buy different pies and mufflers seperate.
all prefrernce.
What are you planning to do to the engine and I can give you a more what you are looking for answer because the options with exhaust can become pretty vast