This is kinda old but I thought I would chime in.
Used tires are great at first. They let you practice alot without blowing a huge amount of cash. But, be aware that used tires are more likely to chunk or blowout because they are usually really worn and heat cycled. You also wont get near as much traction.
Once you can afford it try using the same tire every time. Same size, brand, ect. It pays to get more consistant and always know how the car is going to react. To do this you will have to get a tire that is consistant as well. I have been running kendas because they sponsor our series and are pretty great about hooking us up whenever we need tires quick. Nexen did sponsor us but wasnt as helpful and the tires werent as good in my opinion. I also ran on dunlop dz101's for a while and they are great. The Kendas are fairly close to the same performance for cheaper tho. Ive also run some cheap hankooks that werent bad as well. Falkens are generally good across the board. The cheaper tires wear well with decent tread and the rt615's give awesome grip. I have also run Advan neovas and they made my car into a rocket ship. But, just like the rt615's they dont last forever and are pretty expensive.
For fronts Im using dunlop star specs right now. I have also run dz101's on the front as well as kendas. A stickier front tire will help the car steer into the corner under drift easier and will help with the push problem that our cars sometime have. But, they wear out quicker and are harder on tie rod ends.
Anyway, just a quick bit of info.