Any good wheelbuilder can build an alfine, it’s no different to a normal hub. So just use who you usually would (in my case myself)…
Rim wise, your choice entirely… If you’re light and want to in narrower tyres, you can get away with something light and narrow. If you’re heavier on kit, and/or want to run wide tyres, you’ll need bigger rims. I like the mavic TN719 as it’s not too narrow but not too wide, and it’s a good stiff rim.
Spokes wise, I just used what I could get my hands on, which was some sapim double butted spokes. Anything will do though, but double butted are better. No need to spend mega bucks on bladed or anything though…
If you can hang on til the 11spd finally hits these shores, i’ll be selling my 8spd fully built up on a TN719 with shifter etc as soon as I get one… If you can’t wait til then, 8spd hub is about 150 quid from several places online, shifter about 25 quid, fitting kit 10 quid and a cog about 6 quid… Then a rim and spokes of your choice, plus the wheel build.
On the tubeless tyre front, I’m a great believer in it, others not so much. For me the ghetto system has been totally reliable, though careful tyre choice is required as some are known to be more reliable than others…