For a servo I'd look on/at 9imod or AGFRC servos on Amazon or aliexpress.
Here's my setup with a 9imod 35kg servo on a LCG chassis. You'll have to trim the lower plate for the servo to fit but it'll be fine on a stock HCG.
For shocks id just stick with stocks for right now, unless you want to upgrade the stocks you can get aluminum caps, TiNi shafts, and/or different springs, thinner/thicker oil etc.
For a whole complete upgrade shock set id skip the Traxxas big bores and go straight to the GTRs but a full set plus springs and oil will run you about ~90 bucks.
The 40 kilo animos (red generic) from amazon and a good servo saver. I buy them in 4 packs for about 55 USD. One costs about 17 bucks on Amazon. The servo saver is the important part of the combo. So buy a decent quality one. They cost like 20.