502 is an ok number and the actual number doesn’t matter so much as how you feel. Some guys need to get up over 700 or 800 to feel as well as they want, for other 502 is fine.
Testosterone replacement is just that replacing what the body is not producing and it is meant to be longterm. Watch out for fertility issues if you plan on having kids as T can decrease sperm quality. Clomid or HCG can be used to protect the testicle and sperm quality. It is important not to forget the estrogen as that can increase and needs to be checked. Most men need arimidex to balance the estrogen.
The partition coefficient of the ester in question is important because is effects how long the drug itself stays in the system. If the testosterone transfers too quickly from the oil to the blood, the result is a sudden spike in testosterone which then rapidly drops once the dose has been used up. In the example of free testosterone injected into the muscle from a water suspension (as in Aquiviron, mentioned above), the testosterone is essentially immediately available to the bloodstream due to its low partition coefficient, and thus there is an immediate spike of testosterone which is used up quickly in the body.