Absorption rate of carrier oils: Absorption Rates of Carrier Oils | Beneficial Botanicals
I do not know about 'clean feeling' as that seems too much about perception with is harder to measure.
Percentage of tea tree oil information varies, but IFRA standards for 5B (facial moisturizer is in this category) suggest maximum usage rate of 1.16% (see Link
that opens up a pdf file). But I am not sure what you are actually asking regards 'fats usage rate of tea tree oil'. Do you simply mean the safe usage rate of Tea Tree Oil (the essential oil) with no added carrier oils, or are you asking about the 'oil' that is Tea Tree Oil? As for 'without causing irritation' to acne prone skin, no one can guarantee any one person will or will not be sensitive to any given product (Tea Tree Oil or any other EO, and acne prone or not).
Many sources do suggest that TTO is effective for acne, but again, that does not preclude any possible sensitivities that can occur in any given individual. And of course when used in the presence of other ingredients, determining which are contributing to a particular reaction becomes more challenging.
If concerned about acne prone skin's reaction to tea tree oil, I would suggest trying something very simple first to determine that person's reaction, such as witch hazel + tea tree oil as a toner (like mentioned here
, but I'd suggest you actually determine the percentage used and not rely on numbers of drops) and then evaluating if that percentage works for that person's particular skin. If you're trying to determine if you can make a facial moisturizer for acne-prone skin to sell to the general public, that's another story, as then you'd need to follow Drug regulations per the FDA and that is a big deal. But for yourself or family, then a trial test of TTO with one other ingredient would be the way to go, IMO before formulating the moisturizer.