A/C Help

[nysvx10]

About 2 years ago my compressor went out, and I ordered one of the remanufactured ones on ebay, but have just gotten around to putting it on the car. I just got my new drier today. I noticed on the top of the drier on the things that plug the holes it says "R134A," but I have not converted and still have R12, will this be a problem?

Once I install the drier and put the new belt on, I'm going to take it to an A/C shop. What needs to be done exactly to ensure longevity of the system? Just a flush, vacuum, and charge? Or is there anything else. Remember that the system has been open for two years. Will the seals and orings still be good?Any ideas on how much this might cost?

Ideas/comments?

Thanks
Caleb