new tank arriving soon

[extexanwannabe]

Howdy folks!
I am excited that I have a 115 gal DAS tank arriving in the next couple of weeks. I have been out of the marine tank hobby for several years, and my wife decided to buy a new tank for me.(I just couldn't say no) I have had a couple of DAS tanks  in the past with great success. I have not been able to find out very much about the newer systems. Do any of you have any opinions about the DAS tanks? The two I had were very nice and easy to maintain as far as the filter setup was concerned. My new one will come with 4 T5 light fixtures with waterproof end caps.  The caps are supposedly a brand new design which will allow the lights to be actually inside the canopy of the tank, and won't corrode. I never had that problem in the past anyway, but then there was no such thing as T5 back then.
I am starting my tank with 80 lbs of live rock and 40 lbs of live sand. I have read about NOT to put the rock directly on the bottom of the tank, and yet I have also read to be SURE and put a substrate before the rock. Which is best? I am leaning toward a very thin layer, at least under the rock itself, as I am planning to purchase a batch of "reef janitors" which will include a brittle star or two. I understand that these can burrow under rock and cause avalanches. Of course, these will be added after the tank cycles through. I do plan to put in some button polyps and some mushroom corals. I am having a little difficulty convincing my wife that we do not put angelfish in a tank with corals (sigh). Anyway, I don't plan to do everything at once and will be adding here and there over time.
Any opinions as to the use of "reef janitors"? Any suggestions as what NOT to get? I am thinking I will stay away from the monster turbo snails, but welcome the other snails, conchs, hermit crabs, and brittle stars.