Whether to put the birds on a prophylactic (preventative) course of antibiotics is controversial. Some say it helps more than harms, others say the opposite. A preventative course is given at a lower dosage than a treatment course, so 1 t rather than 3t.
Live-culture yogurt is the easiest probiotic, but don't give with any "cycline" or "mycin" antibiotics. You can purchase powdered probiotics at the health food store (or possibly section of the grocery or drugstore) or at the pet store.
The only difference between wet and dry pox is the site at which the infection takes place. Dry pox is external; wet pox is when it infects the mucous membranes.
So watch any lesions near the eyes, nostrils and mouth. Definitely treat them with iodine or listerine. The sooner the lesion dries up, the sooner it falls off, and the less likely it is to spread to the immediately adjacent mucous membrane. If you do get lesions in the mouth, swab with listerine daily, removing as much gunk buildup as you can--it is the spread and blockage of breathing and eating capabilities that kills them, so if you can keep the passages open, the bird is more likely to survive.
Pox is spread primarily by mosquitoes, but also by mites, lice and direct contact. Spray your coops nightly with a good mosquito repellant such as you would use on yourself (I have considered getting and using the repellant fans you clip to your clothing that I've seen advertised this year if we start having mosquito problems), and separate birds with lesions from those without. It won't completely protect them, but it will lessen the odds of their becoming infected.
