I personally would look at the Gen1 slippers.
http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXBCVS
You may also find benefit to the slipper spring that Kershaw designs has available as the stock one you basically have to run pretty much tightened down all the way.
On my Flux 5B I have some of the alza racing hingepin / tranny braces. excellent stuff but look at some builds to know how they go on.
The high speed idler is very thin, it may chip on you, the one mine came with has a nick on it. Still good but I didn't need all that top speed so if you want it heck I could toss it in cheap with all the savage stuff I won't use.
kershaw offers hardened stock gears as well. Not sure on quality of them though as I am running the regular ones that he hardens.
RPM a-arms definitely a plus including the upper links.
Personally for motor selection I would see if you could find a Castle 1518 1800Kv motor if it will fit your chassis. My Savage when in XL trim had this motor in it. Very high torque, runs cool, and can do 4S or 6S easily and pull the gearing. thats the big thing you want. Having a high Kv motor pulling alot of weight can smoke them pretty quick. I now use a 1520 1600Kv motor on 6S.
Avoid integy stuff other than the carriers. Make sure and get the TCS or Tony screws long bolt for the rear carrier if going integy. Much better than the hingepin you get from them. Tony's screws are a bit cheaper. I also would replace the stock screws with Tony's cap head screws in as much places as possible.
For shocks, seen people happy with the Losi LST ones. I use the HPI big bores as that is what my truck came with and they appear to work well.