A corals-first marine tank...
I've discussed this a couple of places, and some people are doing it, but let me put forward the advantages and the problems---if you have done or are contemplating doing it, chime in. It's at least worth a consideration, counting how prevalent parasites seem to have gotten in the hobby...

Pros
You can start setting up right after cycle.
You put your cuc in, dip, (do a short observation after dip for zoas, particularly) put a number...

How secure do you WANT your rockwork?
My answer is 'not secure'. I balance, prop, lay it a bit like decorative brickwork, but what the ancients called 'drystane' or dry-stone, despite it being underwater. This means I rely on natural balance, I make my arches out of post-and-lintel and rely on gravity, and I do everything I can that way.

Why? Why not make it one rigid form that nothing can ever shake?

Because I have had to go in and do a fish-extraction that...

Do you need fish at all?
Short answer, no, not really.
Many people assume corals are the hard stuff. Some are. Many are so easy you have to be careful or they'll be like crabgrass.

One of the problems people have as NTTH folk (new) is assuming fish are tough. Most marine fish aren't that tough. Not all corals are. But some corals are kill-them-with-flamethrowers tough.

Corals do emit waste, but moderately so. They'll live on light (literally: their colors...

What's (structurally) a safe tank..buying...and buying 'used'
This comes up now and again---somebody trying to buy a used tank.
Acrylic or glass---both kinds of tanks have their cautions.
Acrylic scratches easily, grain of sand getting stuck under a magnet scraper---glass not so much.
Acrylic unsupported by bracing can, over years, bow outward with the heat and weight of the water and sand. You can deal with this, generally, but do be sure that the acrylic is thick enough...

1. be very clear when talking pipe or hose whether you are talking about inside diameter or outside diameter. They use both measures.
2. don't sweat leaks in any join that's meant to be underwater.
3. use teflon plumbers tape on any screwon joint. Wrap the tape in the same direction as you screw on.
4. pipe connects to pipe with a slip on or a screw on type connector. Slip-ons are NOT fastened if always underwater. This includes your downflow. If slip-ons are used outside of...