I bought this lock for my ebike: https://www.amazon.com/gp/product/B07KVFRHNK/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
I imagine any lock is fine for the playa, but if you're building a badass ebike you'll also want to ride it around town, and this will help keep it safe. I brought mine to the playa last year and frankly it's faster to lock the back wheel than a cable, I didn't mind using it as much.
Also, if you're feeling less like building your own, I bought a used Sondors Original fat tire ebike last year for around $500, it did great. Bought some cheap 5V LED strips off amazon and a cheap USB charger and that was enough to keep me extremely well lit up for 2-3 days before it needed a charge. It's a simple setup, and the sondors is a champ on the playa.