Go spend a little time on
www.ttora.com and you'll quickly figure out that Tacomas wheel VERY well. Buy one with the rear e-locker, put a small lift on it to run 33's, get some sliders to protect your rockers, and that thing will cover 90% of the trails you throw at it. Either model will get you through moderate terrain without any trouble. To your specific questions:
pre or post 2005:
pre-2005 are smaller and more "nimble" - more of a true "mini truck". Double Cab only comes in an Auto tranny. 3.4 is one of the most proven and reliable powerplants out there.
2005+ gives you a more comfortable cockpit and room for 4 to ride comfortably on long trips. 4.0V6 has nice power, and you can get a 6 spd manual with the double cab.
Long wheelbase has its advantages and disadvantages. Breakover is ****ty, and getting high-centered is more common. You learn to drive the two sides of the truck: the flexless IFS, and then the longer (but flexy and locked) rear. But you get good stability with the wheelbase, and on some rocks/ledges/waterfalls the long wheelbase helps.
Just get something in your price range and go have fun with it. You can't go wrong with a Tacoma.