So I have been racing 1/12 on and off for about 10 years and have seen a lot of changes. One thing that I have learned in regards to picking a chassis is that is nice to buy one that other local racers use and that you can get parts for. For me this has been the CRC or Associated cars. I am currently running the CRC Xti and it is great, not saying the Serpent is bad there just isn't any support for it where I race.
As far as picking an ESC the ones with the built in booster are the way to go. Like the 1-2s Orion R10, Hobbywing 1s, Viper, or LRP SXX/Flow.
Motor - currently the fastest one we have found (17.5 blinky class) is the D3.5 based motors like the ones from Trinity, Fantom, EAMotorsports.
Batteries - More capacity and a higher C rating are good, they give you better average voltage through the run, which is important in an 8 minute electric race. Fantom, Reedy, Orion, EAMotorsports, Thunder Power... They all make great batteries.
Servo - make sure you get a good high quality servo your car. Airtronics SGR-HR or 94761, Futaba 9650, JR 3650 are some good recommendations.
Tires - Pick a brand that you can reliably get and stick with them. CRC and Jaco are usually the most common, I personally like the CRC tires better, more compound options on lighter wheels.
Bodies - for stock racing the Protoform AMR or the CRC/Black Art Audi R8C. The CRC is a little less stable but lets the car rotate a little faster, try them both and see what one you like better.
Other little things to get would be TQ 16 gauge wire for the motor, and one of their sensor wires. Super flexible so it helps to eliminate the wire from tweaking your car. A tweak board it nice to have. MIP, Integy and Hudy all make one that will work with a 1/12 car. You don't really need to buy a setup system for a 1/12 car (the Hudy one), a good set of calipers, ride height gauge and a camber gauge are all that you really need for setting one up.
Hope this helps.