I have a comment on the 2HP pump for the waterfall, I seriously doubt it needs to be that big. I have a 3/4HP pump on mine and it flows a lot of water. I can adjust the flow to the waterfall as it's got two outputs, one to the waterfall and one back to the pool. You can lower the waterfall output by diverting more water back to the pool. So far I can make it run like it's got a high flow stream by diverting half the flow back to the pool.

As for the autofill they installed one on my pool. The only danger I can see is that it has a valve on it that can be prone to cracking due to freezing temperatures. I have to put a towel over it if the temperature gets too low. It does have a bleed valve for this but a towel is quicker and more effective. You can turn the water source off to the autofill and then this way only fill it when you want to. The mechanism is very basic works like a toilet, just a float valve.

What I wish I would have done differently is watched the plumbing of the spa better. They didn't put any return lines to the spa so I have to run the jets to get the spillover.