If you're getting to 500 microns the system is most likely leak free.
Usually you can hit much lower than that on a smallish system so it is possible that your vacuum pump is somewhat challenged. Is the ballast valve (if it has one) closed?
Some vacuum pumps are very fussy about the oil level while operating.
500 isn't bad if it holds it for a period of time.

I think I still have purging to do on the compressor.

The micron reading doesn’t go down smoothly, it jumps around after about 2500 (like 1200, 1100, 1000, 1100, 1100, 1100, 900, 800, 700, 800, 900, 900, 900, 700, 600, etc), and while I can pull it down to 400 before I run out of patience, it will then slowly rise up to about 600-700 and stabilize there.

It only does this when I’m vacuuming the whole system - if I isolate the lines, they vacuum down smoothly and stay down.

I “think” that means there is still moisture or oil in the compressor . Maybe a couple more nitrogen purges.