eBike technology explained

Hey everyone!

I've been deep-diving into custom eBike builds lately, specifically trying to understand the nitty-gritty of how all the components really interact. I'm planning a new hardtail mountain eMTB build for some gnarly trail riding, and while I get the basics of motors and batteries, I'm finding myself a bit lost on the more advanced tech.

What are some of the less obvious but crucial technological considerations you've encountered when building your own custom eBikes, especially regarding motor controllers or advanced display integration? Are there any specific tech explanations you wish you had known before your first custom build?