New to eBikes - where to start?

Hey everyone!

Just joined the forum and I'm super excited to dive into the eBike world. I'm looking to build my first eBike from scratch, probably converting an old mountain bike I have lying around. My main goal is something reliable for a 10-mile round trip commute on paved roads with some moderate hills, plus some weekend trail riding. What are your go-to recommendations for a first-time DIY builder when it comes to motor kits (hub vs. mid-drive) and battery selection? Any tips on avoiding common beginner mistakes would be awesome too!