You may want to be careful getting 2 clowns. If I were you I'd go for 3.....2 clowns often tend to fight.
For the lion hiding....What I always do is build a cave that way he is hiding from light but still very visible and my lions ALWAYS take to the cave. Here's what to do get two big pieces of base rock and 1 big flat rock(check the deminsions of your tank and the rock so you don't buy a piece that doesn't fit

) Then take the two base rocks and put them down INTO the sand make sure they are really stable. Then, set the flat rock on top. I always like to center the cave and build to the left and right off that and it kinda makes it and the lion a centerpiece.
No, you shouldn't need to much lighting. Actually the less lighting you have the more you may see the lion out. But it will help grow cool stuff on the LR with good lighting...so you'll want to find a good medium.
Yes, it is possible that the lion will eat shrimp crabs and snails....I've been lucky and most of mine just eat the shrimps. There have been a few of ine who didn't bother with any of it.
You will want to keep a couple battery powered air stones around in case the power does go out. You may want to change 1 gallon of water out every hour or two and put in water warmer than what is in there by 4-5 degrees. You'll want to dump the in SLWLY and away from fish if possible.
Yes, That should be suffiecient filteration.
You can cycle a salt water tank with live rock instead of fish. I usually just buy the uncured LR if possible because it is cheaper and you won't have any fish in there anyways. (And it helps move the cycle along)
Hope that halped

good luck

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Clint
CDevoe1111@aol.com