RE: Next upgrade...
 

AM Hi flows (cat converters) can be had cheaper than that. I know I've seen them for around $100, but of course you will have to have a pro install (weld) the sucker.That could be another $100. I suggest going the extra mile and flanging both ends to meet up w/whatever catback system you choose. That'll help keep things where they should be, avoidblow-aparts, and make it easier should something behind the cat need replacing at some point. I'm a big believer in flanged exhaust systems.
A good shop could match up anything to nearly anything. Your concerns about mixing and matching are well founded.Quality products should work well w/each other. That's my best advice to you here.

RE: Next upgrade...
 

If a header is where you"re headed (pun intended,) and one is available from Vibrant for your application, I'd go with it. Again, they are not street legal, but the best of the best from what I've seen... and I LOVE my Vibrant cat-back.
A lot of ppl like the Magna-flow and it seems to be one of the systems of choice right now. My own experience with them is that on the Mazda 2.3L the are a little on the rough sounding side. Not ricey, just kind of raw, as are the HKS, though they are much louder than the others I mentioned. And the Mag system does not have the prettiest tail pipe tipeither. It looks too much like the OE, IMO. Again, I'm in love w/my Vibe.
Comp radiator? Nah.
Oil cooler? You live in Wisconsin, right. Nah.
Overflow canister? A lot "o" money for a pretty thing, but it is pretty.

RE: Next upgrade...
 

Most manuafacture web sites have a feature to add you cars year, make, model, and engine. Then in matches you wilh what ther make thats compatible, that what the prior links are mainly. Alright, so is $500-750 a reasonable assumption for a good exhaust or is it higher? I have read some good thing about the magnaflow cat-back exhaust system but the tips are 4" and tht seams pretty big to me. Some thing in the 3.25"-4" is what I am thinking 3.5 would be pretty perfect.

Research is my middle name wen it comes to major purchases,

RE: Next upgrade...
 

Good to know the cat-conveters can be found cheaper than what i had run across. And I am most certainly not worried about paying for quality instillation thats a must in all cases. Now headers, why and what makes some of them not street legal or for "off road use only" as stated on so many web sites. I would really like to stick with legal upgrades if at all possible. I will most definaly look into vibrant a little more as well.