Is there a waiting period recommended for getting Botox after Blepharoplasty? Only 3 weeks PO, but I'm anxious to get started

Usually there is no reason not to do Botox after blepharoplasty.
However after lower blepharoplasty, particularly when the canthus has been tightened or a cheeklift has been performed, it is best to wait 3+ months. The reason for this is that some lower eyelid surgeries performed through the lower eyelid, or cheeklift procedures can weaken the lower fibers of the orbicularis muscle.
Botox could further weaken the orbicularis fibers, causing a lag in the lower eyelid and drooping.
It is best to talk to your surgeon to see if any of this applies to your procedure.
There should be no reason not to perform Botox injections in the frown muscles for any of these procedures.

It is acceptable to have Botox injections three weeks post blepharoplasty surgery. Injections of Botox will have no effect on the results of your blepharoplasty.

Jen-Jen,
Three weeks after your blepharoplasty it is probably alright to proceed with Botox treatments. By now, most of the major swelling has subsided and your periocular muscles are probably regaining their activity anyway after being traumatized by the surgery. So, you will need to reinstitute your Botox soon. It may even serve to enhance or prolong the results of your blepharoplasty. Good luck!