I have three rim suggestions, with comments:

Sun CR-18: inexpensive, strong, not particularly flat or round -> spoke tension will be a bit uneven, and takes quite a bit of time to true.

Alex Adventurer: a bit more $ than the CR-18, better tolerance control -> faster build, more even spoke tension than CR-18.

Velocity Dyad: my favorite, round and flat, fast to built, easy to true.

Regarding nipple tool; take an old spoke, crush the threads about 2 or 3 in from the end, so that a nipple can only screw that far onto it, thread nipple onto the old spoke backwards, dip in lubricant, push thru rim, thread onto spoke, grab nipple, unscrew tool. No lost nipples.