It is hard to tell your specifics without putting eyes on it, but if this property was winterized in the past and it had no freezing problems then you should not have a problem.
Sounds like you have the compressors setting down, but staying under 80-85 psi is good.
- Make sure all water sources are turned off and the main drained down.
- Locate the blow out connection, so just cut a tee in or a quick coupler.
- When you first put air to the system, have a valve blow open by the clock or manually.
- If it is a big system, we blow the last valve to flush the main to speed up the zones and to avoid reversion or holding water is sections of the main.
- Take a small hand pump since at times you will have to pump out the water that does not drain from air or naturally.
In the end, do not be a afraid to cut a tee or drain in if you feel it is needed. On our large commercial systems, we will shut the system down, let it drain and then come back to blow the lines. Makes no sense to put thousands of feet of large main with the compressor and I feel it is much less strain on the pipes.
Someone may have mentioned this, but one major thing to remember is the air from the compressor is going to be HOT. So combine hot air with cold pipe and rubber gaskets you can do some damage.