I too would stay away from that ebay kit. A T4 family wheel would cost $100 about anywhere you can find one new, and a rebuild kit costs about the same. So getting both along with the comp cover, and backing plate for the same cost is too good to be true.
Dont forget that you need to properly size your comp and turbine wheel for YOUR aplication. If you will be able to handle the boost that the T4 comp wheel will flow, the stock turbine wheel will most certainly be a cork in the system and you will need to upgrade that too, which means that you will need to get your turbine housing machined for the bigger wheel.
By the time you are done, you could pick up a reasonably priced hybrid from one of the many good shops out there for less than it would cost you to pick up all the peices and then send it out to have it balanced.
In response to the balancing debate, there are some turbos which have the wheels balanced individually, and those that are balacned as an assy. It is said that the balanced assys will have a ground compressor nut on them. Personally, the cost of a new turbo far outweighs the $80 to take it to the local deisel truck shop and have them send it out for balancing. Things tend to go very wrong, very quickly at 150K RPM.
For a decent writeup on rebuilding a garrett turbo check out
www.gnttype.org I believe it is in the how to guides section.