Tummy tuck - previous PE. Am I too high risk?

Your health history does put you in a higher risk category. More information is needed to determine if it is "too high". Meet with your hematologist to discuss your interest in plastic surgery. You will also need medical clearance from your primary care physician or whomever manages your diabetes. If clearance is given on both accounts there are still other preventative measures that will be taken to minimize risk as much as possible.

All operations incur risk; the question for you and your surgeon is whether the rewards justify the risk. A history of pulmonary embolism highlights your risk of this problem with surgery, and any surgical plan should consider steps to decrease this risk.
A hematology consult to determine if you have a blood disorder that predisposes to venous thrombosis should be considered.
Limiting your surgery to either a tummy tuck or a thigh lift may decrease your risk.
A venous ultrasound should be performed prior to surgery to confirm you aren't already harboring a thrombosis.
Measures during and after surgery, including extended (one month) blood thinners, hydration, mobilization, compression stockings, and repeat ultrasound of your legs should all be considered.
Finally, a reflection on other potential risks is important. It is common to become so distracted by obvious risks that the little things can be missed.