I
definitely do not have an answer. I have only seen the website and have not seen the materials, have never trained a child in this method or any educational sort of capacity what so ever.
However, based on my limited understanding of psychology and learning, I'm guessing that if a child can count to 50, that same child can perhaps start to learn the concept of addition and subtraction. I don't know how the nurtureminds book does it, but would guess you'd want to spend A LOT of time talking about what numbers constitute 5 (ie, 5+0, 4+1, 2+3, 3+2, 1+4)... or the concept of "friends" 1&4 are friends; 3&2 are friends. I would do a lot of work just playing around with manipulatives such as marbles or how aangeles used play-doh to make 5 small pieces of clay and then illustrated the concept of combing them to make a big 5 piece... i happen to like the idea of using a 5 marble ziplock bag like in the video seen here: (because it's easy to see it's a 5 piece and there are still 5 pieces)
http://www.youtube.com/v/50C2T8zM3o4&rel=1It sounds to me like all of the children you described would be ready for some level of work. The goal would be to meet them wherever they are and get them to where they could go through the coursework in the nurtureminds (a book I have not seen mind you).
As for how many pages per day... don't know.
BUT, doing semi-short sessions and doing them more frequently will allow someone to learn deeper and faster overall while also maintaining some sanity. Even Doman talks about doing brief but frequent sessions with EK; I believe this principle works well into adult hood as well (except we can go a lot longer than 10 seconds ha ha ha). In other words, it's probably better to do a little bit every day than do a whole lot one or two days per week. Maybe when they get better it might work just as well if they do less frequency and spend more time in each session.
all of the above is hypothesis based on how I know I learn best; your mileage may vary though and I'm not saying it's optimal... so hopefully someone else can chime in with their opinions.