The snapping was due to the fact they can't see well when they are getting ready to shed, totally normal.  The pooping in the water bowl is pretty normal too, he/she was probably in there soaking and just didn't feel like getting out.  Just make sure you clean the bowl really good so he/she doesn't end up with a parasite.  As far as the growth rate I haven't owned a boa myself, but I have heard they are not fast growers (in comparison to corns).  A lot of it depends on how often you feed him/her, but don't overfeed just to make him/her grow faster, they can become overweight.

Keep in mind when the eyes are cloudy they can't exactly see.  So between a new environment, not seeing, and being pulled out and touched, I would expect a snap or three.

A boa's growth rate is controlled by a number of factors.  That being said, the breeder that sold you your boa was giving it to you straight.  I, myself, have a female boa that was born in March of 2009 that is just shy of 5 feet long.

As others have mentioned, most snakes are more prone to aggressive behavior when they're in their pre-shed cycle.  When you see that they've begun their shed cycle, it's best to leave them alone until they've completed it.  This is not only for the keeper to avoid bites, but also for the snake's welfare.  They strike because they're scared.  If they're scared, they're stressed. - And a stressed snake is prone to all kinds of problems.

And yes, a water bowl poo is nothing to worry about.  It happens as often as not.

+1 kcb couldn't put it any better