BTA stands for behind the axle steering, it gives you better approach angles because the steering rods and servo horn are now out of the way and behind the axle, the unit with the servo on top of it is call a dig, it allows me to lock up the rear axle so i can make really sharp turns as well as a lot of other things, but we can get into that later, as for weight in the rear you really don't want any but the battery would be better placed there then up high in the chassis making it very top heavy and more prone to rolling over, what you really want is a forward bias weight distribution with a total weight of around 6 pounds, one of the reasons your rig likes to flip over backwards is because with the weight of your battery up high like it is the weight starts to shift back as you climb up a rock and make the rear wheels dig in so it is pushing the crawler up the hill more then it is pulling it causing the back end to dig and grab more flipping you over, one of the other things that I did to my rig was put under drive gears in the rear so that the rear wheels spin slower then the front which makes it pull going up hill that much more, I also run plastic wheels with no weight in them at all so the rear is really light, another advantage to this is it allows me to get the rear of the crawler to pop up over things and kinda float behind the rig instead of dragging it down. As for shocks i am really liking my Duratrax shocks that i have on it now. But the length of the shocks would be determined by the chassis you are going to run, and just about any chassis would be a huge improvement over stock. There is so many things you can do to make these rigs crawl better it is ridiculous, I hope that helps answer some of your questions, we will be here to help get you up to speed and make good choices on what to buy and what not to buy.
