2000 Ford Mustang v6 Reliable?

So I'm looking at a cheap 2000 mustang with 75000 km's (46000 miles) but I'm a little scared of how it will be, the owner now has replaced a few things so that they're new and it seems it has been decently taken care of with there being a little rust on the fender so should I go for it and buy a 17 year old car? They want under 2 grand for it

Music system upgrade in Ford mustang 2017 (base model)?

So, I was thinking about getting my music system in Ford mustang 2017 (base model) upgrade. The music system it came with is pretty decent but I want more bass. Is there any way that I can only get its sub upgrade.
I have Harman Kardon home sub-woofer system too, Is there any way that I remove the sub from its box and install it in the car? I know its kindda dumb idea but I know that its one sub is enough to give the car a bass boost.
if not, is there any cheaper upgrades out there with some good bass? I'm talking around 1k-1.2k including price and installation.
getting music system upgrade, will it void car's 5 year free warranty by ford?
One last question is, Will it impact on car's battery? Will it drop the life span of the battery?
What are the problems can arise with bass boosted system?

again, I'm talking about good bass that you can feel enough not like one of these systems which makes your whole car shiver.

Upgrading mustang v6 2017's exaust/mufflers

So, I got a new mustang v6 2017 and I heard that you can upgrade the exaust to make it sound like v8. So, my question is how muc does it cost to buy a new one and getting it installed? Any cheaper ones out there with some decent quality? Does upgrading exaust/mufflers drops mileage? Does it drops horsepower? Does it impacts the engine anyways? Does it has any impacts on its 5year free warranty by ford?

Is a 1970 ford thunderbird easy to fix up?

I've found a pretty good deal on one but it's missing motor and tranny. I've found those too, but I was wondering how hard it would be to do this. Also, is it possible to put a 2005+ drivetrain from say an impala or mustang or something in it? I want it to be so I have to fix it less. Don't worry, not changing interior or anything. Just the stuff under the hood.