Lady G, looks like your are trying to paint a color portrait with only black and white.
One of the first things I have noticed about salt tanks is that they all resemble stacked rocks LOL. There is only so much stacking and arranging you can do with the rock.
In a FW tank, your options increase tremendously.
That is why I started to make my own rock. It is easy, fairly cheap, and you can make the most awesome caves, pedestalls, swim throughs etc all custom to fit your tank. I may make a poodle and then find something to grow and cover it like a chia pet.
It is absolutely safe for fish and corals. If you plan on keeping a tank for the rest of your life, you may as well start now with a good rockwork base. Over the years you add and watch things grow on the rock you made. You seed it with the small rocks you already have, then remove the small rocks to the fuge or sump.
Oh sure there is some joy in buying a nice rock with great life on it, but if you start with a small frag today, it grows over the course of your life and if pruned you can aquascape your tank to perfection.
A word of caution on large sculptures. If you ever have to move or get a fish out, it can get very difficult. It's not like you can pick one rock at a time and relocate it and its inhabitants to a temporary tank.