Its not essential to lock the rear diff, it will give you great slides but can ruin the Track ability of the TC4 should you want to race.

For Drift, the Tamiya TZ and RZ motors are a good start

a Trinity Komodo 19T is also a motor to watch out for.

I have drifted with Both a Team Orion Method R 19x2T and a Team Orion Method R 15x2T and both are great..