Since they make 24h disc hubs, I assume (with some reserve) that it's possible to build reasonable 24h disc wheels. HiLo flanges make some sense for rear wheels since they help reduce the tension differential on dished wheels (the benefit varies with the number of crosses), but I can't see a reason for them in the front since most front disc hubs have the same ctr-to-flange distance on both sides.

As far as reusing spokes goes, many people do, I don't. Then again by the time I rebuild wheels they have enough mileage on them that I feel I've gotten full value from the spokes and rims. Reusing spokes is a judgement call, based on how much use they've seen already, vs. their cost and the value you assign to your time. If you do reuse the spokes, try to keep them sorted by outside (head-in) vs. inside, because the elbows will have a different set accordingly, and it'll reduce the change in set with the rebuild.