Now Crosseyed!

I was reading through the beginners section untill I got crosseye with all that information and everything that you have to take into account for a supurb sounding system.
That would be great, but at this point in my life I realy do not need anything fancy, I just want something to improve the sound quality in my truck.
2002 Dodge 1500 quad cab.
Alpine CDE 7659 45wx4 with base engine.
Stock speakers in all 4 doors.
The system sounds pretty good for stock wires and speakers.
Im looking at installing a sub to give it a little more punch in the low end for now.
And maybe upgrade the 4 speakers in the doors in a year or 2.
I dont listen to blasting music, if it hurts I turn it down.
I was thinking that the section under the back seats would be a great place for the amp and speaker/s, Ive seen the cover for turning that space into a sub box but I will probably make one myself.

Anyways, my question is, what would you recommend for me?
What size sub/s and wattage/amprage would I be satisfied with?
Should I go with 1? or 2 subs?
Should the enclosure be ported?
What type and Size (wattage/amprage) of amp should I look for?

I installed stuff like this when I was a kid but the industry has grown almost as much as the pc industry and I have been out of touch with it for so long I have lost track.

Thanks for the patence and feed back.