Can Botox injections reduce the size of submandibular glands? If so., how many units should be used and how many injections?

No physician would knowingly use Botox instead of lidocaine for numbing. There are two muscles that work on the eyelid. One closes the eye, the other opens it. In your case, the muscle that closes the eye is likely weakened (In fact, we sometimes use Botox to weaken this muscle for people...

Sorry for your injury! Botox should not affect your healing, but I would not be treated again until wound is completely healed. Good luck!

Plucking your eyebrows is safe after botox.  There are No restrictions for that after Botox treatments. It will NOT change the overall neurotoxin's results. 

It is safe to get Botox if you are allergic to penicillin. There is no known cross-reactivity between Botox and penicillin,and a penicillin allergy is not a contraindication to receive Botox treatments. I have many patients who are allergic to penicillin who receive Botox without any issues....

The masseter is a very bulky muscle, and so it does require a higher dose of Botox to relax it than the dosages typically used to treat the muscles of facial expression.  A very typical starting dose is 25 units/side.  This will achieve full treatment in about 80% of patients.