DH and I had the same conversation just yesterday and we've decided to stay with the standard plan, ie I TS, 1CS and 1 snack. We did the same last year and felt we had more than enough.
We have 4 children, DS8, DS7, DS4 & DD3. We enjoyed approximately 10 character meals and that for us was just about right. In fact it got slightly repetative after a while. Dont get me wrong the children loved them and it was great to do every other day which is what we did.
On a seperate note, you need to consider how your girls will be when it comes to the characters. My eldest and youngest loved them from day one, had no problems interacting and thats from the age of 2. Second and middle eldest was scared and extremely reluctant to even acknowledge them till they reached around 4. The exception to this was with our eldest son.
The first time he visit wdw he was 4 and our second son at the time was 2. As it was a first time for me also we booked CRT for breakfast as it was always a dream of mine to do. Eldest DS took one look at the Princesses and bolted under the table not just for 5 minutes but for the whole hour. In fact no body actually knew he was there which was fine by me. He was scared beyond belief.