good advice here.

as stated previously, it's the ERD that is most important, IME. whether or not you wish to reuse spokes and nipples is usually a quasi-safety issue so i won't comment. anyway, if you decide to reuse the spokes and end up with mismatching ERDs. here's a couple of tips.

1) if spokes are a little too short, i've found that extra long nipples can give you an extra 2-3mm to work with. i've seen it stated that it is untrue, but i've used them on several builds and they will help.

2) i've found that if ERDs are even more out of whack, that changing the number of crosses in the lacing pattern can make all the difference. a little luck helps here.

3) sometimes, if the spokes are different lengths on the front wheel compared to the rear, or different lengths from the drive side to the non-drive side that some of them can be swapped around and reused. i've had wheels that had three distinct spoke lengths. you never know.