99tl w/o navi

There are a couple of routes I am considering for a system upgrade. But first, I need some input from the members of the forum.

1. will a 6disc in dash player from an mdx or newer tl fit in my car? The main reason I am considering this instead of an Aftermarket unit is that I would like to keep my steering wheel volume controls. I know about the IR units from PAC. I will not do the line of site thing. I understand that there is another unit PISX or something that can connect directly to the remote input of some decks, but its a little slow. How slow is it? And what brand and models will it work with. Preferably Alpines.

2. I have the OEM acura 6disc changer in my trunk. If I upgrade my factory deck to an aftermarket can they connect directly. I read another thread that says Alpine makes the OEM changer. If so, will this changer connect directly to an Alpine cd player/controller?

3. Ok, the big question. I would like to know if anyone has replaced the rear factory sub with an aftermarket free air sub? I came across a Pioneer TS-W254F that crutchfield sells. Will it fit without much modification? I dont know if they make an 8" in that model, but it might fit better.
I had an mtx 12" in a bandpass box. I took it out due to space. I would like to really try and keep the factory look and not spend a lot of money. How about the Pioneer TS-SW124D Premier® 12" Shallow-Mount Subwoofer in an infinit Baffle application for the factory sub replacement? Thats if they make an 8" or 10" in that model. Or the 8" Pioneer TS-W203F

4. What are some good drop in replacements for the factory front and rear door speakers? Something with great sound, low-midrange price, and easy fit.