subwoofer and mid bass?

Not sure what direction to go in. The more I read about car subwoofers, mid-bass, and enclosures the more I scratch of what I want to put in my new Tacoma. I'm not to worried about space because I plan on loosing the middle portion of my rear seat for the sub-box, and if need be putting the sub-box in the camper shell. Any help with my questions will be greatly appreciated. Thank you!

Question #1, is sq the quality of the sound of the subwoofer and spl how loud the subwooffer is? if SQ is the sound quality will adding more sq subs increase the SPL (how loud the subs are)?
Question #2, can I in stall a combanation of SQ and SPL subs (same brand but maybe different sizes)?
question #3, I have had many after market systems in the past but never had mid-bass speakers, will adding them on this system make a big difference, and can they be installed behind or under a seat?
Question #4, if SQ is the sound quality will adding more sq subs increase the SPL?
Question #5, I have only had sealed boxes in the past, what will ported boxes do for me, will they be more for SQ or SPL?

1 and 4 = YES    2 = YES   3 = YES and Not reccommended. Unlike lower frequencies, mid bass frequencies do not travel properly going through obstructions. 5 A ported enclosure is more efficient at and around the tuned frequency. The trade off is not such a good response at frequencies lower than tuned frequency, and also at frequencies much higher than tuned frequency. Solution is to cross sub amp at a frequency not too much above the tuned frequency. Then use midbass drivers to take care of those upper frequencies.

Ported boxes do more for SPL than SQ, though there are ported setups with good SQ. If you're constructing a ported box with SQ in mind you typically tune the port a bit lower than you would in an SPL system. One advantage of a ported box that may still be considered an SQ trait is low frequency extension (of course, the extent of this depends on the driver(s) used and the box construction). On the otherhand, "cabin gain" will give you a nice incremental boost in the low range unless your vehicles interior is huge.

What type of music will you listen to on this system?