Definitely use rubber isolator pads under the feet when you lag bolt it to the floor. They make a huge difference in noise levels. I cut up an old tire I picked up at the dump and used those for the pads. (The Sawzall had to work getting through those pesky steel belts!!)
As for a hole in the shop wall, don't overthink it. Here's a 1-1/2" drain line I put through my block wall. Some mortar and paint and looks like it was made that way. The drain goes to a 28" deep hole I dug (14"x18") and filled with gravel. It's just to drain a laundry sink I use for washing hands, etc. You can also see one of the compressor feet with a pad under it.
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