Is it safe to have a breast reduction if I suffer from lymphedema in the leg?

Yes. Breast reduction surgery usually does not include removal of the lymph nodes in the arm pit and should not cause arm lymphedema. The leg lymphedema is a separate issue and is best treated with compression socks.
Stable leg swelling. Yes you can, though the normal placement of anti-embolism compression stockings may not be possible. There is always concern about blood clots in the legs with prolonged operations like breast reductions and recent ultrasounds of your legs before surgery would be important. Some form of a blood thinner may be indicated. Your plastic surgeon should be made aware of this condition and will guide you.
Should be. I agree with dr. Aalami, they should be completely unrelated.