Congratulations. I don't think that the strength is critical. I use the 20 PPM Advanced Colloidal Silver. A good home brew should work fine for nebulizing. More than 20 PPM is overkill and anything less and I use 5 ml in combo with 1 ml of lobelia extract per breathing treatment. You can just use a bit more often. As far as how long to continue goes, I would say to continue doing the nebulizing once daily for a week and then perhaps cut back to every once in awhile. And don't neglect the oral silver solution use either, when needed. I personally do not take silver orally except when I think there is a need.
I look forward to your post about the mouth cancer in cats. I may well want to share it with our pets group. Colloidal silver, properly made oleander extract (or oleander supplement) and inositol/IP6 have been an effective combo for many cats, dogs and other fur-friends.
BTW, you weren't dumb. There are lots of things you can take orally that might not be wise to breath. Silver just isn't one of them.