New to eBikes - where to start?

Hey everyone,

Just joined the forum and I'm super excited to dive into the world of eBikes! I'm looking to build my first one, probably starting with a hardtail mountain bike for some local trails and commuting. My main question is, for a total newbie to custom builds, where should I even begin? Should I focus on the motor kit first, or the battery, or finding the right donor bike? Any advice on reliable entry-level components for someone aiming for about 20-30 miles per charge on mixed terrain would be awesome!

Cheers, [Your Username]