Is there any reason to use longer than 12mm nipples (as shown) for building up this wheel?

Looks like a pretty hefty rim bed for an alloy rim. The 12mm works, but I would opt for 14.

The nipple flats are real close to the rim's surface. No mechanical issue but easier to scratch the rim around the nipple during ham fisted truing.

Agreed that the rim looks pretty thick at the spoke bed. What kind/model? Andy

My only reservation would be if you ran out of thread with a longer nipple

It's a DT Swiss R460. On the ones I have, I used 12mm nipples with no concerns.

OP, what hubs did you go with?

That's correct - for the rim model.

It might surprise many but I wanted this a good old-fashioned Shimano angular bearings (RS-400 which I believe is Tiagra as it has 11sp freehub body). It's really all basics, 32 3x J-bent straight 2mm spokes. Out of curiosity I weighted everything and it looks like well under 2kg for the wheelset (excluding skewers).

If you have any lower weight results for other hubs and/or lower spoke counts, let me know how much I have overblown it.

Like I said in the other thread. I used Bitex hubs. The model I used is 85g front and 245g rear. 11speed but I use mine with 10. Double butted spokes everywhere. I'm around 1550g.