Drift Car Chassis: i recommend any shaft driven chassis for drifting. I ran an xray which is belt driven and it kept throwing the belts. I use a heavily modified Tamiya TT-01 now, but don't recommend it. You have to make too many alterations to make it worth it and not many adjustments available... it is cheap though.. a second hand team associated TC3 would work well.
Diff set up is the biggest thing... lock or tighten the rear.. loosen the front diff. If oil filled diffs.. then oil grades... if ball diff then simply tighten rear and loosen front. Spool the rear if available to you.
Note... this is the exact opposite way you would set up a racing car.
Steering upgrades are available for greater steering angles.. google that stuff
Brushless: very good upgrade.. decision first.. race or bash
Race.. i recommend a sensored system (has a sensor cable from the motor to the esc). Then i would get a 17.5T motor as this is the stock racing standard. Hobbywing V2.1 Esc for secondhand, or V3 for new. These will need a programming card and hooked to the internet to upload firmware (there is an awesome thread relating to this on here). Set you back about $120 australian for esc, about $100 for a motor... ebay or for sale section on here.
Bashing.. much cheaper Hobbywing combo EZRUN comes with esc and motor for a fraction of the price. No sensor cable, minimal programming, so plug and play. Can pick one of these up for less than $100.
Note... 1 australian dollar is about 1/2 pound..