There's no hard and fast rule as to whether or not dual exhaust will provide a performance benefit or not. Typically, they are tuned to provide a different exhaust note to increase aesthetic appeal, but that doesn't always translates into better performance.

While reducing back pressure can increase torque, it can do funny things to emissions controls. Lowering the pressure may result in decreased exhaust temperature, meaning your catalytic converter might not operate correctly (or, at least, as well as it should). Dual exhaust also fails to guarantee a drop in exhaust pressure; that is dependent upon a number of factors, including but not limited to the diameter of the exhaust pipes, length of the exhaust pipes, etc. There are Helmholtz resonance issues to tackle, that's the main thing (which, not coincidentally, is what the cross-pipe helps address).

Also worth considering is whether or not this is a 'cat-back' type system. If it is, then you aren't removing the biggest restriction in the exhaust system: the collector and catalytic converter. If that's the case, you may see some slight reduction in back pressure and a slight power gain, but it won't be dramatic. If anything, you'll pick up a nice sound coming from your exhaust and aesthetic appeal in having two exhaust pipes.

Of course, now you have two mufflers to replace and more weight on the car, which may or may not offset any power gains (probably won't). The point is, there are a lot of considerations to keep in mind. The most important thing is, if you spend $300 (or whatever the cost is), are you going to be happy with the aesthetic results? If that's true, go for it. Consider any power gains a bonus; certainly don't expect to turn your car into a 1/4 mile machine.

And Remington, a MAF sensor makes perfect sense. It detects how much air is being pulled into the engine and calculates the correct amount of fuel to inject as a result. If the sensor was giving funny readings, you could run too lean (or too rich) and have a rough idle or simply stall on idle.

That depends.  What kind(s) of driving do you intend to do most?  How many people/how much stuff do you intend to haul?  What are driving conditions where you'll be driving?

Oh sorry. Thanks for the quick reply though!
I live in a suburb of Ohio (Midwest USA).

I think a normal sedan sized car would be alright.

I'm trying to avoid a truck, because my mother seems to think that they're dangerous enough that if you come within ten feet of one, (insert bad thing here).

But a normal sedan should be alright.

Question: what is the difference between a straight-6, a flat-6, and an inline-6? Are they just interchangeable terms, or are there significant mechanical differences between the three?

I'm assuming that what you call a slant-6 is what we'd refer to as a V6, for much the same reason.

The V allows a more compact engine lengthwise.

I may have missed this, but is the exhaust you're buying the whole thing from the headers back (headers, downpipe, back to the mufflers), or is it just from the downpipe back.  I don't know if this holds true for all cars but I with my car switching from stock exhaust manifolds to aftermarket headers will free up a decent bit of HP (Somewhere in the range of 25-30 I think); however leaving the stock manifolds and just changing from the downpipe back really doesn't do much good at all until you're producing somewhere around 300WHP.   

That's the best advice. Sounds like the motor is shot and not producing enough torque to lift the window up (windows can be heavy). Not exactly sure why the window would slide down on its own, but replacing the motor should fix your issues.

Thanks for the info.
I kind of thought that's what you'd say.

Unfortunately I don't have the patience to rewire a motor BUT, I do have lots of tape.

  That's a tough one....depending on how deep the scratches are...  If they're not deep at all, you might try some 1500 to 2000 superfine grit paper or rubbing compound and rub it out, then polish it with some chrome polish.