How exciting to be taking your little ones to Disney. We have been going every year since our daughter turned 3 (now 11) and it can seem over whelming (all the planning, packing, traveling, and spending time in the crowded parks).
As far as Ridemax goes, I would not purchase that plan. We tried it when one year when my daughter was 5 and it just didn't work too well. It was o.k. in the beginning of the day but we really found ourselves running in different directions all over the park based on expected wait times of rides and the plan/itinerary it had us follow. In the end we felt rushed, wound up exhausted, and didn't ride as many rides as we had hoped or what Ridemax said we could accomplish.
Here is a link that explains Switch Pass pretty well. http://wdwuntangled.com/fastpass.php.
3 day Park Hopper is ideal and I would definitely use it to obtain the Magic Morning benefit. IMHO Magic Morning is definitely worth it especially for children in the 3-7 age group. You will have much shorter lines for popular Fantasy Land rides that are perfect for your son and daughter. Get to the entrance before rope drop and I would head straight to Peter Pan's Flight first as the line there can get rather long even in the morning. If you are lucky, the lines won't be too long and you will be able to ride that twice without much waiting. After that, you are right there to hop on Dumbo, Tea Cups, and my daughter's favorite Mr Toads Wild Ride. If your husband isn't keen on rides like Dumbo, Tea Cups, etc. he can go get fast passes for other rides (ie Space Mountain which you would do the Switch Pass for your daughter) while you and the little ones ride or wait in line.
Not sure if they still do story time with the Princesses in the castle but that was a highlight for my daughter when she was younger. One year, we ran into Prince Charming on the side of the castle after story time and my daughter got to spend 15 uninterrupted minutes with him for pictures and a visit. They even did a little dance. He was rather charming and extremely patient and generous with his time! No one else was around and he treated my daughter like a true princess. It was really very sweet, totally unplanned, and a memory we will have forever. Character time was very important for my daughter when she was younger and she enjoyed that more than the rides.
I like your idea of visiting CA Adventure when you first get into town. We usually arrive in the afternoon (fly from Denver), check into the Grand Californian and head over to CA Adventure. We don't even attempt to go to both parks in one day or start DL on our first afternoon. CA Adventure is a great way to ease into the whole Disney experience.
Disney Land/CA can be overwhelming if you try to do all of it in 3 days. I would focus on getting to the parks early (before rope drop) the mornings you can, taking a break in the afternoon back at the hotel (nap, dip in the pool, leisurely dinner in DT Disney or the park). Go back in the evening with Fast Passes for rides you collected before leaving the park in the afternoon and the fireworks show or Fantasmic. I have found that when we tried to do everything and stayed at the parks from open to close we were exhausted and didn't really enjoy it as much.
I can't be much help on the Camelot Inn and Suites as we have only stayed at the Candy Cane Inn (our first visit-which I can't recommend) and the Grand Cali. Being close to the parks is a definite plus.
Another helpful idea is to look at the park maps on line and the list of rides in each area. Make a list of "must do" and take it from there. Know that you won't be able to experience every ride in 3 days but Disney Land will be there for future visits. I know when we go to Disney that we won't be able to ride every ride, get a picture with all of our favorite characters, and spend all day in the park. It's too overwhelming and exhausting to even try. I just remember that I am in the happiest place on earth with the people I love the most and having a wonderful experience.