RE: Truggy quesstions
Front caster would really be more of an individual tuning issue. That said, this is what we learned last year running the Berg unlimited and Pro Hobby Production trucks. I'm sure you are aware that the steeper (smaller) the caster angle the more turning you will get with the tradeoff being stability over rough ground and sluggish jump recovery. With that in mind and given that MT's by design and tires size are slow turners, we started wit the steepest caster angle we could. This provided adequate, and sometimes excessive turn in and the big tires helped with the stability over rough ground, but recovery after jump landing was a real problem. Not that we were crashing off jumps, but that few seconds of floundering were costing us so we backed the caster angle down a bit to see if we could improve our off jump performance. With the Berg we started at 11 deg and moved up to 13 deg. The Pro Hobby trucks are based on the T Maxx so we started with the front upper arms all the way back (both clips forward) and went from there to a single clip on front and rear. Sorry I don't remember off the top of my head what the angle is, but it's the middle adjustment available out of 3. Anyhow, the berg started landing better and didn't seem to give up any turn in so we tried the next option which was 15 deg. Everything still looked good and landing was getting better so we took the final step to 18 deg. At this we lost a lot of turn in and the jump landing didn't improve enough to justify the loss of turn in so we settled on 15 deg and ran them that way. During the course of the season we had a couple of drivers change this up to better compliment their driving style, but no truck ever used the full forward (11 deg) or full back (18 deg) caster option. In the case of the Pro Hobby truck, the middle position turned out to be where our drivers liked it best so we stuck with it. I personally prefer my Pro Hobby truck kicked all the way back, but that's me. Either way, try it like you have it now, see how you like it and adjust accordingly.
As for the 2 speed question, for trucks like the T maxx, it can make a big difference, but i never saw a track where we could get the Berg's up to top speed so a 2 speed would have just been extra weight and maintenance on them. For reference, the longest straight we ran on last year was 263 feet corner to corner.