What weight capacity do I actually need?

Add up paddler weight plus gear and add roughly a 30% buffer. Most tandems in this list rate 400 to 500 lbs; the Intex Challenger and Explorer K2 are rated to 400 lbs, the WETURE and GYMAX tandems to 507 lbs. r/Kayaking commenters repeatedly warn that loading near the max sits the hull low and hurts both tracking and freeboard.