I have sold plenty of things on this forum and it's pretty rare that I hear a horror story. Most ppl on this forum are good guys/gals.
No, buy from www.getbmwparts.com
You can get the standard or GTS (satin black finish) at a great price. I got mine for ~$2250 shipped. Came in exactly 1 week.
You can use the same TPMS from your old wheels. That's what I did, but you will hafta swap them if you want to throw the old wheels on for track or winter unless you can deal with errors.