The challenge associated with gluing on more wood to make a rigid handle is that if the glue you use is not up to the task it can fail when the bow is drawn and the handle can pop off. Whether this happens depends on how much the handle would bend when the bow is drawn and what sort of glue/epoxy you use. I have made a few board bows with rigid handles, and have managed to use Titebond III as the glue and not had problems. These were shorter bows (under 60 inches) and had lower draw weights. If you use a longer curing epoxy of some sort, you would probably be fine. I have never used these, so am not in a good position to make recommendations.
As far as length overall, I have made bows as short as 45 inches from boards and had them turn out well. It is all about choosing the right board, and the right design for that board. I have added both reflex and recurves to boards before, it is just like bending stave wood.
Regarding red oak vs maple, I would say maple is a better wood but finding a maple board with straight enough grain is hard. Maple logs often have twist that you cannot see when the log is cut into boards. This means that you might find a board that looks perfect based on the rings, but blows up when stressed because of all the grain runoff. Red oak is not as snappy, but tends to grow straight and I have had fewer failures with it. If you can find hickory boards, those might be useful too. Hickory also often grows straight, and folks have made amazing bows from hickory boards. If you heat treat it, that will take care of its tendency to absorb moisture and become sluggish in humid air.