Need some opinions
 

So, between wanting to clean my truck up, reading all this about finals being in the (moderate) area, and having cash flow, i want to redo my system.

I have a ford explorer XLT, and currently have 1 15, but wanted to do 4 15"s, but just don't have the space with the seats up for work. I am thinking of 4 12's. My two main options are as follows:

2 Audioque 2200's and 4 12" Fi SSD's
OR
2 Audioque 3500's and 4 12" Fi BTL's.

Of course the btl one is more desirable, it's gonna be pretty damn expensive and i already have 1 2200; but have a buyer if i decide to sell.
Any other advice would be seriously appreciated, and i have chosen these companies because i have used their products and loved them. Thanks.

2 18's have more cone area & efficiency, will drop lower, and are cheaper than 4 12's. You could keep your amp and get two BL 18's. If you can't do 4 15's in 4cf3 each, can you do 7cf3 per 18? Is this a wall? That's $1600+ on subs and a lot of batteries to power 7kw, instead of just spending $600 on subs. If you can afford all that, 2 BTL 18's walled on something like an AB 500.1 would do the trick.

the 12''s will be easier to fit but the 18''s will drop crazy low compared to 12''s. of course this could also be dependent on the box, but my one 18'' went lower than my two 12''s, but the 12''s had more impact than the 18''.

I'm not going to do a wall, but the 18's do sound tempting. I have my 15 on an AB 400.1 now. I would love to go low as balls, like 28hz or something, but would also like to hit some decent numbers. If i can make enough money, i would get:
4 BTL 12's
2 AQ 3500's
4 NSB 90's
New alternator.

Also, if this car does deside to crap out on me at some point, the 12's could fit into a trunk, as a 15 is hard, and an 18 is harder.

That's like $5000. These are upfire, right? You can't fit 4 upfire & sealed 18's in 20 cubes can you? Are these taking up the entire rear? That'd hit low as balls. 4 SSD 18's are $920+options+shipping and in 5 cubes the tune is 42-44hz (the 2010's). Fully loaded they'd be perfect for an AB 400. If your car dies, you could always buy a hatch and lay them over the folding rear seat. Why no wall? You could always get a ballin' rear camera. I'm planning to put 2 2010 SSD 18's behind the front seats of my Alero in a 10 cube sealed wall with an SAZ 1500, I can't wait!

Do the 4 12inch BL's and poo your pants..

with an AQ 2200 for every woofer

...or just get 6 18inch steve meade woofers and blow your windows out.

do DC subs dude, not on back order and you have LOCAL support.

I have 6 12's on 3k in a 97 4 door exployer right now. Fits in the hatch and under the window line. 7.5cubes tuned to 40ish. Needs more battery though. Still does the trick. Before retuning the box it did a 147.7 sealed at the dash. Hit crazy lows.