Bad idea to have contrast ct & contrast mri in same day (i.e., too much, different contrast at once)? should i request creatinine test 1st?

Your doctor?: You shouldn't have to be the one to think of that sort of thing! Do you have one doctor who is aware of both studies? If in doubt, get a second opinion.

Radiologist: Your radiologist is likely to test you for creatinine, especially if there is any doubt about your renal function. Beyond that I would rely on the judgment of the radiologist.