can you use a regular airbrush system with food safe colors?
If it is brand new and never been used with any thing else.
I'd maybe put a filter of some sort on the compressed air source. And I probably wouldn't use an old spare tire as that source.
the airbrush gun is brand new, but the compressor is used. does that matter? Do i need to clean out the lines or brush with anything special
As long as the airbrush is brand new, this will be fine.
The compressor supplies the airflow through the hose and into the airbrush via a one-way valve, so a pre-used compressor will be safe to use.
If the compressor is fitted with a moisture trap, then this will capture any moisture from within the hose. Compressors without the moisture trap will need the hose to be disconnected, between use to allow the moisture to be released so you do not encounter what is called pulsing during use, which can effect your decorating.