Just built my first rim, a rear one installed on a gear driven hub motor. After installing the spokes I put the wheel back on the bike for truing, which only took a few minutes as I had been pretty careful while assembling. After truing I installed the tire, then began tensioning the spokes while checking for true on occasion. The bike itself worked fine for me for a truing station.
2 thoughts. First, regarding the rim, most rims on the market are set up for 14g spokes (regular bicycles). Most e-bikes use 13g, with a few even using 12g. The holes in the rim are sized for nipples appropriate for the the spoke. Point being, you are likely going to be dealing with a new rim set up for 14g spokes. There is an easy work around in the form of special nipples that can use a 14g hole in the rim, but are set internally with 13g threads.
2nd thought, you may be able to use your existing spokes over again if they aren't too cruddy/corroded.
Last, I bought my spokes (and nipples) from wheelbuilder.com. They are really quick to cut and ship custom lengths, and are fairly priced. Good people....
Pay attention when measuring for the proper spoke length!!!! Custom cut spokes are not returnable for any reason.....
Because of my weight (300lbs), I used a single butted 13g spoke. These spokes are much heavier near the hub - which is where they always break.
I would recommend the purchase of a tension gauge. This will eliminate any guesswork regarding your final spoke tension. The Park Tools gauge is pretty expensive. The one I bought was half that price (about 40.) and served my purpose just fine. -Al
