What do doctors consider when looking at the amount of immune suppression drugs used for a kidney transplant patient?

Many Considerations. There are many issues that can affect the amount of immunosuppression given to a recipient. The relationship between the donor and the recipient, the specific donor kidney source, the age of the recipient, the liver and bone marrow function, prior use of immunosuppressive drugs, prior cancer or infections, are just some of the medical variables that play a role.
Risk vs. Benefit. Since you don't come with dials for us to read to tell us how suppressed your immune system is, we use clues to interpret what is really happening. Indications that your system is too suppressed are infections and cancers. Too little suppression allows rejection to happen. We start your regimen based on factors such as how different you + the donor are, + how vulnerable to rejection the organ is.
Several things. Immunosuppression with medications are essential for optimal functioning of kidney transplant. There are several serious side effects due to these medications. Doctors look for any occult infections, liver function, kidney function, blood counts, none marrow activity etc.