New to eBikes - where to start?

Hey everyone!

Just joined the forum and I'm super excited about getting into the eBike world. I've been looking at a lot of pre-built options, but the idea of a custom build is really appealing – being able to pick exactly what I want. For someone completely new to this, wanting to build a commuter/light trail eMTB, where do you even begin? Is it better to start with a good donor bike and add a kit, or go full frame-up? Any advice on essential components or pitfalls to avoid for a first-timer would be awesome!