Is there any shallow area on the rainbow river where someone may park a kayak and go swimming or snorkeling between the KP hole and rainbow river canoe & kayak?

When I was there, we went swimming and snorkeling at various points, and used support from other boats to climb back into the kayaks. There are a few pull-off points along the shoreline where you could park as well

Yes

Yes, lots of great little dive places

Yes there are a couple of spots

When you start out from KP if you go left there is a sandy area on your right. You can stop their and dock your kayaks. Their is a cool little river you can walk down. It is beautiful and mostly just sand.