FYI, the smaller the F number (like in photography) the faster the system. A 3.3" mirror is indeed a small mirror although I have a telescope that has a smaller primary. When you start getting mirrors this small, you start running into problems with getting enough Field Of View (FOV) to fully illuminate an EP. A .66" secondary is is barely large enough to give a 100% illumination to a 25mm EP on-axis and you might want to use a larger secondary. It might be an interesting design to put the secondary on the side of the tube and use the primary in the Herschelian mode. The coma may start becoming visible but the light gathering will be better and the contrast may be higher with that arrangement. That range is in the grey area of what is better. The project will be a fun one with the kids tho.