A few tips:
Plenty of horizontal space is very valuable. It may sem hard to believe starting out, but prime space for mounting frags & having enough room for growth can run out quickly. Try to resist the temptation of buying boring corals and mounting them in the prime spaces.
Keep plenty of sand bed open. You will be surprised how many corsls need this environment like scolys, plates & others. It also helps with an open natural look. Watch out for star fish. Some are predatory and a pain to keep.
Don't make structures too high. If you go higher than about 2/3 of the tank height, this may be too bright for some corals and if they are of a branching variety they may not have the room to grow, even if they can handle the light. But this advice depends on the tank dimensions and your lighting power.
However you stack them or support them, keep in mind you may have to remove the rock one day to catch a fish, remove algae etc. so don't engineer it as one connected structure that can't easily be taken apart.
Don't let them touch the glass panes as it will be hard to clean. Leave enough room to accommodate the magnetic cleaner of your choice.
Make sure the structure is stable. You can arrange the LR so that it interlocks or you can use fiberglass rods drilled into the centers for support. Reed putty isn't very effective for this purpose IME. Don't be afraid to saw the LR in the bottom course flat. It will be stable and with a ~1 inch sand bed you get the appearance of a coral head protruding from the sand bed as opposed to just a few boulders stacked on the sea floor.
Good luck, have fun.
