Spoke Tools

The first phase of wheelbuilding can use a screwdriver-like tool to tighten the spoke nipples, and this is much faster than the later phase using a spoke tool. The classic screwdriver tool looks like a regular screwdriver bent into a right-angle Z. I have no doubt that a seasoned builder could use such a tool with admirable efficiency, but as an occasional builder I haven't tried to find one.
Instead, I ground down a standard hex screwdriver bit, as shown. I used the edge of the grinding wheel to leave a pin in the center, which fits into the spoke hole in the center of the nipple. This works far better than a standard screwdriver bit because it keeps the bit centered and allows the bit to hold the nipple fairly well. (This shape is borrowed from the classic tool.)
I like this bit a lot. Its small size makes it a nice handle for inserting the nip and engaging the spoke, then a finger-roll or two engage enough threads to move on to the next. I can't think of a tool design that would make this process faster.
Later, after all spokes are installed, I use the bit to perform initial tensioning, until I need more torque than fingertips can provide. Then I put the bit into a small ratchet driver and work until that too becomes slow. Then the rim strip goes on for safety and I switch to the standard spoke tool which works on the flats exposed next to the spoke (and visible in a finished wheel).

Spoke Lengths

It finally happened: I laced a wheel with the wrong length spokes. I noticed just after lacing, before any time spent tightening, but still a costly mistake in time and money.
The main culprit is the database in the on-line calculator tool I found. I believe it thinks an M756 rear hub is centerlock, but it has the large flanges that come with an ISO rotor mount. I share the blame, though, because I didn't check the dimensions before I bought the spokes.
In the good old days, say around 2000, there was a functioning on-line community in rec.tech.bicycles which put together accurate and complete tools for this as contributions to the world. These days profit-seeking seems to have destroyed those tools and replaced them with hit-and-miss or deliberately incomplete tools.

I bought the first set of spokes from an LBS which cuts and threads spokes to length. While this ensures the length is correct, the cut ends are very sharp and the threads less clean than the factory rolled ones. They're also more expensive, perhaps due to the labor of cutting.
At the second shop, I asked them to check my revised calculations. This is the most modern shop I deal with, in the sense that I get good response to email. Their calculation was even more wrong than my original set. This time I think the rim size was incorrect, though the lookup matched the sticker on the rim itself! I got a look at the calculation process at this shop, too. For the last decade or so, I've used spreadsheets or web calculators, and electronic databases of dimensions for the hubs and rims. Here there was a programmable Casio calculator taped and zip-tied to the inside cover of a binder holding pages of dimensions. (I suspect much of these are out-of-date by now.)

In the end I re-learned the old saw, measure twice, cut once.