eBike technology explained

Hey everyone!

Been lurking for a bit and finally decided to dive in and start a discussion. I'm really curious about the nitty-gritty tech behind our custom eBike builds, especially when it comes to matching components. For those of you who've built your own from scratch, what's been the most challenging or surprising aspect of getting all the different tech (motor, controller, battery, display) to play nicely together? I'm thinking about a new commuter build, maybe a hardtail MTB conversion, and want to make sure I understand the tech compatibility before I start ordering parts. Any war stories or success tips?