[RC-Monster Mike]

Supermaxx,

Welcome to the forum! I see you have what sounds like a great truck that is near bulletproof! This is definately a good platform for a brushless power system. I will try to touch on all your questions in this post (not necessarily in the order they were asked:)). First, there is absolutely no need for a dual brushless system. The complications of running dual systems far outway any advantages (I can't really think of any advantages!). In answer to your questions about the dual systems - yes it can be done, but my suggestion is don't bother.

If you want to run a 12 cell set-up, the Fegao 8L or 9L or the Lehner basic xl motors are the best choices (xl 3100, 3600, 2800 all work well). The 8L and basic xl 3600 should be limited to 13 or 13 cells total, so if you are thinking you may someday want to use more cells, go with a 9L or xl3100 or xl2800. The Lehner xl motors are very similar to the Hacker c50 (xl 3100 nearly identical power delivery), but they are lighter and have many more options for gearing (as HotnCold mentioned -c50 size limits gearing). The Feigao "L" motors have a bit more torque than the Hacker c50 or Lehner basicXL motor, but have there disadvantages as well. The Lehner motors have a fixed endbell, which makes them the low maintanence, plug and play choice. The Feigao motors have a pressed in endbell, which may require some additional thought and preparation to make it as bulletproof as the Lehner motors (not hard to do, but something to think about). You should be able to select a gear ratio and leave it alone. No need to change gears unless you change your driving needs (short track vs long track, tire change, etc.). Which brings me to a question for you:
What do you want to do with your truck? Do you race? Bash? drag race on the street? 45mph is pretty easy to accomplish, but driving at that speed in an e-maxx is fun for about 8-12 seconds, then stopping comes into play, or turning. We gear for about 32-38 mph for most tracks and find that speed is never an issue, nor is torque. It all depends on what you want to do with it, how many cells you want to run and things like this.
As far as suspension goes, I have or have had just about every suspension kit ever made for the maxx trucks. I love the racer x suspension and its handling, but I love the g-maxx suspension as well. The g-maxx has a lower CG and is lighter, as well as being less expensive. The Integy suspension is the best buy for the money (racer x handling at lowest price of all aluminum premium type suspension). They all have their strengths and weaknesses. If you and your friend like the racer x the best, then clearly its features suit your driving style, so stick with it. Like I said, they all have plusses and minuses and I don't think you could go wrong with any of them.
For pinion gears: the 8L and 9L (and all Lehner)are available with a standard 1/8" shaft , so any pinion gear will work. I only recommend the 1/8 shaft for 12 cell applications or less on the "L" can motors, as the additional torque and weight of more cells puts the shaft at risk of breaking). I also have a few 5mm bore pinions (14, 16, 18 and 20 tooth) should you go with the 5mm shafted motor. For speed controllers: The 9918 will accomplish what you need for a nice price, while the upgraded micro controllers have more capability and slightly better software. Hopefully, I answered your questions or at least gave you some things to think about. If you still have questions, by all means, ask away! Welcome to the forum!!