If you were to go to a 20 inch wheel as you would on a bicycle like a Bike Friday, running a 36 spoke wheel is akin to running a 40 spoke touring wheel in a 700c.

The 36 spoke wheels on my 20 inch touring bike are insanely strong and I am building up a set of 28 spoke wheels for lighter touring.

Smaller diameter rims do not need as many spokes to deliver equivalent strength and at your size you might look at a 26 inch wheeled bicycle with 40 or 48 spoke wheels... this is what we use for our tandems and larger single riders.

Since I am a lightweight rider (145 pounds) I built my touring wheels on custom hubs (36 spoke) laced to CR18 rims and even when I am locked and loaded my total weight with the bike would not touch 225 pounds.

For you I'd build 48 spoke wheels laced to even stiffer rims... we have been very happy with Salsa Gordo 48 spoke rims and have one 400 pound customer who has been trying to break the 48 spoke disc wheelset we built for him for almost three years ago... they have never needed to be touched with a spoke wrench because they were built right.