"Tubulars" actually do have tubes (at least the vintage ones), it's just that the tire carcase completely envelops that tube, and is sewn up with a seam that lies on the tire-side surface of the rim, onto which the tire and tube are glued. A clincher captures the tube between itself and the rim, with beads (either steel or kevlar reinforced) that hook into "bead hooks" on the tire edges of the rim. Don't buy older clincher rims lacking "hooks", which are still around -- get ones with definite hooks. If you're looking to get into electric power, then get wider rims and tires. The recommendation for the Velocity Atlas rims is a good one. Several manufacturers make more heavy-duty rims. Also, if you want disk brakes (I think I saw that), then there are rims that are made specifically for disk brake wheels, rather than rim brake wheels (they former have no braking track on the rim sidewalls). I guess you might be able to fit disk brakes on a wheel with rim-brake rims, but why bother?