as far as "custom length" spokes go, i never even bother with that. just get a standard size that's a little bit longer, lace it up, then grind the excess off.
every wheel i build, there's always a few spokes that stick above the nipples a little (enough to pop a tube) so i gotta grind them off anyway, so if there's 36 spokes with 2 or 3 threads showing, it ain't no big deal. takes about 10 seconds a spoke to grind them smooth.
as long as there's enough threads so the nipple doesn't stop before it's tight, there's no problem.
for the average guy, though, it's not really a required skill. if what you want is available already laced up, go for it, or if you get a good deal, go for that, too. unless you're building a lot of bikes or custom configurations, i wouldn't worry about learning to build wheels.
truing them, though... everyone who owns a bike should learn that...