Tire Foam Question

Need advice on a servo to purchase.. I havent run rc in 7 yrs. the last time was on dirt and in SC 1/10 I used to run savox and spektrum servos I have no idea what i will need in a buggy with high traction carpet. My son will be running a Yokomo yz2 cal3 on a Sanwa mt44. Until we can upgrade he will be running a Tekin Pro esc and a 17.5 redline...its what we got I am looking to buy a Kyosho RB 6.6/7 or a Yokomo yz2 CA2/3 what ever i can afford. With same same n motor. i however will be running this on a Ko Proppo as thats what i got until i can upgrade radio. ive been looking at protech servos as they have good reviews on amain...but would like opinions and advice as I know the servo is important especially on such a technical track... Any advice is appreciated cheers

Do you have transponders for sale on location? What do you recommend? Would something like this work? The description says that it is not compatible with AMB systems.

What would be a good starting point for front and rear springs for a light-weight rwd buggy? I see some of the set-up sheets you have on this forum, although, I'm having a hard time finding the lb. rating for those springs. Thanks a bunch.