Yea! Glad you stuck it out! There are tons of supportive people here. it is hard to read 'tone' in the written word, and some misunderstandings are bound to happen...
We had good luck with the high-pitched "yipe" and "ouch" to get Denna to stop mouthing us. She still will put her mouth on us, but very, very softly. She also likes to jump - hopefully you won't have to work through that... for us it was an over-excitement issue, which she's now finally grown out of (she's a year old now).
"leave it" and the "its yer choice" youtube video might have some good things for you to work on - helping the puppy learn self-control, and how to take treats gently.
I have hopes of getting Denna into therapy, too - although, not to the level you're taking it. I bought a book which has a bunch of great advice on things to work with for preparing a therapy dog. There are a bunch of books out there if you haven't gotten tham all, already.
Cayeessmon has some great advice, too. Not having kids myself, I'm at a loss on the best way to get kids to slow down for the puppy and not entice them into play... or how best to get the puppy to ignore the excitement of little kids.
I do think the EM is a great choice of breed for your son. Their gentle, calm nature was what attracted us to the EM, also. Their loyalty and smarts are major bonuses that we're learning more about every day.
I wish you well on this challenge!