The Mamba system is a great. I haven't used their stuff in a while but the last system was not waterproof. They might be today but I would contact castle creations and ask them.

The 3800 or 4600 are both a good fit for the Rustler. If you are running stock tires or close to stock sized tires you should start with about a 15 or 16 tooth pinion and monitor motor temps using an inexpensive temp gun. You want to keep motor temps below about 160F. Adjust gearing to maintain motor temps. If it's too hot go down a tooth. If it's not hot enough you can go up a tooth.

Yes the 3800 with bolt directly into the Rustler.

Yes his non-lipo batteries will work but they won't be the best performance or run time wise. You should also monition battery temps. If the batteries are too warm to touch then the more is pulling too much from them and they should be upgraded. Again, Gearing will help here as well. If too hot then go down a tooth to take some of the load off.

Any controller will work fine. 2.4 is just less hassle if others are in the area. Also gives considerably more range.

No programmer needed.

A couple of other things you need to know. If your rustler is an older model it could still have the plastic gears in the trans. Upgrading to the VXL idler and diff should be considered mandatory with brushless. Buy a couple of bags of Stub axles. They will break if the truck has any kind of real traction. Deans or traxxas connectors are also mandatory. If ou truck has the old molex/Tamiya style connector it should be changed.

I've owned a couple of dozen traxxas cars and trucks over the years and i've managed to work most of the bugs out of them without breaking the bank. If you need any further help feel free to drop e a line.