New to eBikes - where to start?

Hey everyone!

Just joined the forum and super excited to dive into the world of eBikes. I'm completely new to this, and honestly, the idea of a custom build really appeals to me – I love tinkering! My main goal is something for weekend trail rides (mostly gravel and light singletrack, 20-30 miles at a time) and maybe some light commuting. For those of you who've built your own, what was your absolute first step? Did you start with a donor bike, a frame, or just a motor kit and build around that? Any "wish I knew this" tips for a newbie looking to build their first eMTB?