generally, when it comes to alloy upgrades I like to use alloy on these parts:
motor mounts (if the stock one is plastic)
diff cases
steering hub and steering knuckles
rear wheel hubs
shock towers
shocks (or sometimes just shock caps)

IMO, all other alloy upgrades are just for looks.

For me, wrenching on RC's is half the fun. It doesn't matter if you are a backyard basher, or a racer....or if you have a $100 truck or a $600 truck, stuff will break. Ive literally had over 400 rc's by this point. I buy/sell/trade a lot. HPI, kyosho, losi, redcat, traxxas, duratrax, Tamiya, axial, ect....ive had something from all of them. They all have good/bad points to them. For me, it has always been about fun-to-cost ratio. with redcats, I generally found I got a good amount of fun for my money.

I think your manual has an exploded view of the model. Generally that is all I ever need to tear a model apart and put it back together. For some who have a harder time, use a digital camera and take pics as you begin tearing it down. That way you can look at the pics if you get lost when putting it back together.
The important thing is to take your time, and make sure not to lose any screws! I don't know how many times I have wasted 10 minutes looking for that screw that rolled off the desk and blends in perfectly with the carpet