If you're set on a three-tier system, go for it. However, have you considered a two-tier system with a pump? That would let you keep the overall height lower. You'd be able to fly sparge if you want, and you can use the pump for a variety of other uses - like recirculating while chilling, or pumping to your fermenter. I'd suggest that you try building a a mock-up of your system to try the height dimensions you're thinking of. You could do that with a ladder, table, saw horses, or whatever is handy. I did a brew session with a mock-up of the system I'd been thinking about to see how it worked out. It was very helpful to actually brew on the mock-up because I found some things I'd like to change, add, and delete from my design.
I've been working out the details for converting a salvaged factory cart to a brew cart, and I've settled on a single-level system. I batch sparge, so I'll only need one pump - which I recently got as a holiday gift. The cart will have two burners on one level, and a folding shelf on the end to hold a mash tun. I might even try to design the shelf so I can tip the mash tun for emptying. I settled on a single-level system because I won't need to lift very much, or have hot water up high. I also want to be able to look into the top of any of the brewing vessels without using a ladder, stool, or mirror.