I have a 3 level (4 grids high) NIC cage for Korr (4.5ish pounds) and Amelia (3.5 pounds). Both can get up and down easily. They don't use the top level as much, but I think that is more as there isn't a ton up there. The bottom level has hay and the litter boxes as well as the door out and the middle level has pellets. They tend to hang out the most on the middle level, I think because they like the view and can see more. The bottom is 2X3 grids, middle level is 2X2 and top is 2X2 with an extra one to make 5 grid floor.
I have steps so they can get up and down easily. The highest one is 1 grid high and the others are about 1/2 a grid. I have it set up so there is no more than 1 grid between steps in case they were to fall, it is not as high. Each step is supported by an L shelving bracket. The levels are supported with wooden dowel.
I would say for safety, support everything and make sure there is not too much of a fall from any point. Some rabbits have a harder time jumping up, so more steps or ramps may be needed. Have something fro grip as well so they don't slide around when jumping up or down.
Large breed rabbits may need more support on levels to handle their weight better. They can also have harder times jumping up and it can be harder on their joints, so ramps may be better or have lower steps.