I'm going to build a wheel with 650B rim (VO Diagonale) and a front hub with unusually close together flanges (SP dynohub, center to flange only 22 mm). Should I worry about the spoke triangulation angle? Should I build to higher tension to compensate?. Any reason to prefer 2 vs 3 cross?. Spokes will be butted, like DT Competitions.

U worry way to much, do as any wheel and 3x. Done.

I wouldn't worry. With the smaller ERD of the 650B rim it's really not that extreme. Rears run worse angles than that all the time on the drive-side and the lateral forces on the front wheel are significantly less than the rear. There's no conclusive evidence that 2x vs. 3x has any effect on wheel stiffness on a rim brake front wheel, it's simply trading a small increase in radial load on the hub flanges for a small decrease in weight from shorter spokes. As for tension, once you have enough tension to keep the spokes from unloading, additional tension has no benefit.

tl; dr: Build it the way you would with any other hub and you'll be fine.

Glad to hear this. I was even thinking about choosing a rim with offset spoke holes and lacing the right flange to the left spoke holes and vice versa. But that seems extreme.

I'd probably cross 2X, but mainly because I've never done 2X and this seems like a good enough excuse to try it.

EDIT-
You didn't mention how many spokes. 32 or 36.
I'd be more inclined to go 2X on a 32 spoke wheel vs a 36.

In a 32 hole 3 cross is Like 4 cross in 36 hole- 1st cross is the spoke on the other side of the flange,
headed to the opposite side of the rim.
Hook is pulling into the most aluminum between the hole and the edge of the hub flange.

You can always Mix cross patterns. Say 1 less on the Non Drive Side. which will of course be Under less tension.

Because it is a Hybrid Freehub-IGH...

If a 1 cog IGH there will be little if any Dish..

No. The drive side of rear wheels is worse and works fine.

No. Wheel tension has no effect on stiffness.

Number of holes, spoke bed diameter, and hub flange diameter - you want the spokes as close to tangential as possible for strength, and don't want to overlap the heads which would complicate replacement.

As a roadie I've only dealt with 700C / 622 rims and lack practical experience on where smaller rims like 650B / 584 need fewer crosses.

If it's not a disc wheel and you really care about more spoke triangulation and if the hub can tolerate it (I love three 'if' statements), you can always lace it radially with all the spoke heads in to maximize the triangulation (and fugliness).

Ditto by me. Front wheels are way overbuilt. I have a 24-spoke on my SWB recumbent and it's never been a problem... and you know I ain't small.

FWIW, J: are you still collecting oddball French parts? I saw a set of CLB centerpulls in the used parts bin at CCC on 17th today.

Thanks. I'm not looking for those, though they are cool. All parts acquisition is focused on the Phat Bike.

I'll agree with the others, it's a front wheel, no worries about the bracing angle.
It's true though, those SP hubs are tiny. I've just started dealing in them, have a couple here. I would be very interested in your experience with it from a performance point of view. I have one built into a wheel for a demo, but other than hooking it up to a light and giving it a spin in the truing stand, I have not tested it. The claims of lower rolling resistance seem to be accurate.