One thing to keep in mind is how much water will be above the pool level. I don't have check valves on everything. I usually have my jandy valves set so about 75% go to pool returns, 25% goes to the spa to keep it circulated. When the pump is off, the levels equalize. Check valves can prevent that, but check valves can also fail. If the spa is too tall, and it drains down, you run two risks: plaster drying out in the spa, and pool overflowing.
That said, I wish my spa (and the pool, too!) had a raised edge. Anything on the patio is fair game to end up in the pool. Even 2 or 3" would keep a lot of small stuff from blowing in.