Acceptable vacuum levels are determined by the effects on the tissue that they are acting upon. By all means, start with low levels and track your results. You should only increase levels if you become conditioned to lower levels and will benefit from higher levels. Don’t be impatient, all vets will tell you that gains take time. If you start jacking up vacuum levels without giving a low vacuum program a chance, you’ll likely injure yourself.
With that said, don’t let anyone tell you that higher vacuum levels are unsafe to the veteran conditioned pumper. I have been pumping for over a decade and routinely pump at 5 - 10 Hg, followed by segments at 10 - 15 Hg. I stopped getting the donut effect years ago and have a consistent and satisfying pump at those levels with no spotting and no freakiness in tissue distortion.
The most important thing I have found is to begin with lower vacuum levels (and ideally some heat) until you pack a tube with minimal lymph buildup and good EQ. Then go to the next higher tube size and work into that. In my opinion, a .25” difference is too much with a packing strategy. So I fitted a 2” tube with a insert made from a 1.875” fish gravel cleaning tube. I cut it to length, leaving about half an inch protruding. I then dipped that for 15 seconds or so in boiling water and using an oven mitt, formed the then malleable plastic against the outer tube in a bell shape. The silicone ring then fits over the whole setup nicely. That way I can move from 1.75” to 1.875” to 2”. I am very satisfied with my results.