Do I have to wait very long after breast reduction before conceiving?

Conceive First. Recommend completing pregnancies prior to having breast reduction surgery. Filling of glands for milk production (even if not breast feeding) enlarges the breasts. After return to normal, additional loss of native breast fat and sagging skin is a common result. By waiting until no further pregnancies are planned, then deal with reduction and lifting as needed.
It depends. Ideally someone who was planning a breast reduction and a pregnancy would undergo the breast reduction following the pregnancy. In the setting where the reduction has already been performed two months should be sufficient time to start planning a pregnancy.
At least a year. It takes a year to a year and a half for scars to completely heal after a reduction. Breast enlargement during pregnancy puts tension on the scars which can make them moe visible yielding a lesser result.
After healed. Dr alexander is correct that you should have babies first then reduction. If you have already had the reduction surgery and now want to get pregnant, you should wait until your breast are fully healed, probably at least 3-6 months.