Ime, it isn't any more complicated than other apparently-complicated rebuilding tasks - e.g. checking big-end plain-bearing clearances, wiring without making short-circuits? Bit daunting before the first time but, these days, plenty of YouTube how-to's.
Only things they don't always stress are:-
. Take lots of photos. of the spoke pattern - close-up into the hub, into the rim and in between hub and rim - wheel component suppliers don't always get things like nipple dimple angles correct for Spagforth Whippets and similar.
. If the old rim is apparently where it should be relative to forks, swinging-arm, hub, centreline, blah, measure and compare "offsets" or other manual references to reality before you start to dismantle; not unknown for some manuals from in the last century to contain misprints ...
>the price for error seems very high
How so? Financially, wait 'til you have a wheel that needs rebuilding, then it'll be cheaper than having someone else rebuild it, because your labour is free.
Also, it won't be pot luck and potentially more than one trip to the wheel-builder to get the rim where reality says, not where some manual misprinted in the last century 'says'.
>how tight does one do up spokes
If you're that way inclined, view this an opportunity to acquire more shiny tools; e.g. a spoke torque wrench?
>should any thread be left showing on the spoke?
What does your shiny new torque wrench indicate?