I'm also a newbie to A/C to. If you suck down the R12 system into an old propane take, will the R12 / air from the system settle in the propane take so you can vent off the air and leaving the R12 in the tank so you can reuse it ?. I have several old refrigerator compressors I could use to rig up a recovery system. When you use propane, is it 100% propane or a propane / R12 mix ? Also can you use a compressed air line oilier to inject oil into the vacuum side of the vacuum pump filled with mineral oil to keep the pump lubed ?
R12 and air won't separate out like oil and water in a propane tank. Separating refrigerant from air is something that is almost impossible for a person to do without specialized equipment.
If you're recovering refrigerant from old appliances, you should evacuate all air from the lines and tank before puncturing and recovering from the appliance system. That will keep your air ingestion to a minimum.
R290 is refrigerant grade propane, meaning it's pure propane gas. BBQ gas isn't as pure as r290. You'll have to look up specific refrigerants to see what their composition is. I'm unaware of any refrigerants that are an r12-propane mix.
A compressed air line oiler won't work to inject oil. It's very likely that the o-rings and other pieces inside of it aren't rated for refrigerant use. I wouldn't worry too much about oiling the suction side of a vacuum pump. In my experience, most pumps have their own lubricant and lubrication system, so more lube isn't needed.