New to eBikes - where to start?

Hey everyone!

Just joined the forum – super excited to dive into the eBike world. I'm completely new to this and looking to build my first eBike, probably converting a hardtail mountain bike I already own for some local trail riding and commuting (around 10-15 miles each way). What are the absolute must-knows for someone starting out with DIY conversions? Any specific motor types or battery considerations I should be prioritizing for reliability and a good balance of power/range without breaking the bank? Thanks in advance for any tips!