If you already have the kettles, lay it out on the floor and be sure the Brutus plans will work. Masking tape works great for this. The overall structure is pretty simple. Big rectangle that holds 3 vessels. Set your tallest vessel on a table. At that height, can you easily look in to it, see it, stir its contents? If not, go lower. Consider the height casters will add.
The welder that did my stand didn't want anything to do with ensuring the air tightness of a gas beam like the one used on the Brutus design. Hence, my iron pipe plumbing.
If you are going with flexible plumbing, make sure there is a good way to support your burners. Some people use the black iron pipe to hold the burners up. My burners actually support my plumbing, although it would be easy enough to secure it to the stand.