This is part of my setup. You'll find what works best for you over time, but I started out with large metal shelving units, the ones they sell at Costco that look like they are from a restaurant supply store. Those worked okay, but I find that having more shelves that are narrower works better for me than a few deep shelves. I cannot reach the plants in the back easily if the shelves are too deep. So I bought these units in the closet supply area of Lowe's and then bought hardward that would attach them to the sides of the greenhouse. They are adjustable and are plastic coated, so they do not rust. I can hang the lights from them and can easily move the lights around. I found that having things as easy to move as possible was a good idea because from year to year my needs changed in terms of shelf height, etc.
Another trick I learned somewhere, which saves on heating bills, is using a large heat mat on the shelf. This is very easy to make yourself. If you want information on how to do that just post and I'll do photos for you. It allows me to keep a low heat under the soil of tender plants without keeping the entire greenhouse heated too much.
The other thing I do to save on heating in the winter is I put long sheets of polycarbonate across the ceiling . I still get the same amount of light, but there is no need for me to heat the dead space at the top of the greenhouse. I don' t have plants hanging down from that high. Like yours, the walls of my greenhouse are taller than I am, so the polycarbonate is well above my head. I'm heating much less space that way and not wasting energy.
