So many questions..
Nah but seriously...
What do you recommend as far as the different engine options?
2.2 and 2.6 carb motors from 84-86, no real reason to buy unless the rest of the van somehow justifies it.
2.5 tbi, super reliable and easy to work on, but hopelessly gutless with auto, only acceptable with manual.
2.5 turbo, ~400hp bottom end from the factory, ~200hp top end. It CAN be the easiest of them all to get power from, but with the auto your mileage will be horrendous. 2.5 turbo +5spd FTW imo.
3.0 known to have BAD valve guide issues 87-92 or so. Otherwise very solid engines.
3.3/3.8 are two versions of the same engine and basically have no major weak points. They are rock solid.
Which one you get depends on what body style and wheelbase you want.
For hop-up potential, the turbo 2.5 and the 3.0 are the easiest to get major power increases from. Either motor has been over 500whp from someone in the turbo mopar scene. The 3.0 is a little harder because it isnt turbo from the factory but n/a mods can get you to 160+whp. That doesnt sound like much but with a 5spd you're talking low 16s, high 15s in a caravan, not terrible. 3.0s never came with 5spds but you can mix and match factory parts to make it a complete bolt-in affair.
As for gas mileage, the 5spds take the cake. You could get 2.2 carb, 2.5 tbi, 2.5 turbo with factory 5spds and swap the 3.0 pretty easily. The only 5spd that bolts to the 3.3/3.8 is pricey, rare, and more difficult to install.
Otherwise pretty much all of them should do ~20-22 mpg with auto if driven nicely. I had a 3.0/3spd that got 25 but i dont know why.
The AWD system has never been broken with power, it's super beefy. On the other hand, AWD only CAME with 3.3/3.8, and people generally dont mod them because people are lame and dont see potential in anything that didnt come with a 5spd or in a light car.
The factory awd system has been adapted to a 3.0/5spd but its power limits still have not been tested.
As for mpg, i would think an awd auto 3.3/3.8 van is mostly going to avg under 20 mpg.
They never made a long wheelbase manual van from the factory. All long wheelbase vans other than a handful of factory freaks got v6s, and v6s never CAME with a 5spd. It is possible to get a long wheelbase 3.0 and swap it to 5spd. Here's one with a turbo. http://www.youtube.com/user/splatmaster86#p/a/u/2/2atLBT3xCXs
As for potential swap candidates, depends on what swap you mean. motor or tranny? Turbo 2.5 swaps are easier into 84-90 vans because of wiring, but still possible in 91-95. Swapping to a manual trans is about the same difficulty from 84-95.
I completely forgot to mention the 2.4 that came in 96-up vans. It only came with 3spd auto and is a dog from the factory, but since it's the same basic engine as an srt-4, you can imagine the turbo antics that are possible from that engine. I dont personally know of anyone who has 5spd swapped one of those yet.
http://www.youtube.com/watch?v=78InPT4iqlw&feature=player_embedded
Sport package on the 2g 91-95 vans is.. bumper covers, sometimes side moldings, fog lights, sometimes monochrome paint, and a rear sway bar. I dont know which engines you could get it with.. Thats all i know for sure on those. On the 96-00 ones there is more than one version but still bumper cover, fog lights, honeycomb grille, monochrome, liftgate spoiler, 16s or 17s, higher stall torque converter, rear sway bar, and sometimes autostick. I THINK you could only get sport package with 3.3/3.8 on those 3g vans. I dont know anything about the interior stuff that comes with it other than that 3g sports tend to be highly optioned and have leather and captain's chairs.