Upgrade when you break is the best advice. Lots of learning to do first before slapping in expensive parts only to crash and break. Those 3.3 engines are junk so if it were mine that would be the first replacement. Then the CVD's.
Aluminum shocks on that thing will cost ya a small fortune using 8 and IMO not worth it. Will they make it ride smoother, maybe but it's a MT, not a race truck. Not my truck tho, spend how you wish;)
With the power you'll be putting through that trans, there is nothing to worry about in the plastic gearing dept. As mentioned before, you want that point of breaking on a cheap $3 part like a plastic spur gear.
I wouldn't buy a new 3.3 engine or even a free one.
Put another .19 dynamite in your rusty. It'll last 7-8 gallons. A 3.3 traxxas engine is about a .19
I had the same set up, but this was 13 years ago or so.
Had a Picco .26 in it too.
Fun MT's for sure! Especially when you go 1/2...