New A/C System Charge Questions

I have a '74 Charger with a 440 and factory air that I just finished putting back together. All of the A/C components are relatively new or have been replaced. Rebuilt RV2, new hoses, evap and condenser are fairly new. Compressor has no oil.

Here are my questions:

1.In a system like this, would I be better off converting to R134, or sticking with original setup? If I keep the R12 setup, I only have Freeze-12 available.

2.Would it be necessary to flush system in either case? There may be traces of Ester oil in system. Can Ester oil be used with either setup, and how much oil should be added to dry compressor before charge?

Thanks in advance!

1) Freeze-12 is mostly R-134A. R-12 is readily available but pricey, with all new components the wise thing to do is stick with R-12.

2) A new system will take 10-12 ounces of oil. If you're using mineral oil, a little residual ester will mix with it no problem.