Don't even think of going with low spoke count wheels if you intend to lose weight after you start riding - unless you want to get more excercise walking than riding. If you are heavy and inexperienced you are far more likely to break a spoke or get the wheel out of true/round. A low spoke count wheel will go farther out of true from a broken spoke and typically be harder to true. In return you save a few ounces at best.

Some folks obsess about extra weight on the wheel, forgetting that the weight difference generally coming into play is a very small percentage of the total. Your bike in use will not weigh 21 pounds, or 24 pounds, or even 30+ pounds. The weight underway is the bike's weight plus yours. Even for a svelte rider we're talking about 150 lbs, but more commonly around 200 lbs. That means if you save 4 ounces per wheel at the rim and accept the old saw about wheel weight meaning twice as much as static, the effect is one pound out of 200, or 1/2 of one percent. If you are getting the bike for excercise rather than Olympic level competition what is the point?