Wow, everyone must be at the WMAS monthly meeting because nobody answered. Well, it's 9PM here and I need to get to bed so we can get up at 5 to go snorkel around hoping to see some Pocillapora spawn.
First, let me welcome you to the WMAS Message Board. This is a great place with a lot of helpful people.
Drilling the tank to install bulkheads to make an overflow system for an RDP Refugium is the best way to go but I have done many simple tanks without any sump/Refugium. It's all up to your budget and need for speed.
I have never used nor will I ever use anything but sand on the bottom. I don't know where the idea of placing eggcrate on the bottom came from but it's not a good adea for many reasons that I don't have time to discuss right now. In all my experience with aquariums, I cannot think of any time that a rock broke the bottom of an aquarium when it was sitting in sand on the bottom.
Getting the levels right is a no brainer. Just mix up a good marine salt preferably, but not necessarily, with purified water.
There will be many more things to learn. It's really best to do a lot of study, ask a lot of questions and then do something I could not do when I first started this hobby in 1993. Use this MB and go see some people here and ask them to explain how they do it and why. You are also in luck because the Annual Reef Tour is coming up soon. It's a great way to see a lot of tanks in one Saturday.
Enjoy and feel free to post more questions or call me direct for immediate opinions.