Legal regulations for eBikes

Hey everyone!

I'm diving into planning a custom eMTB build – thinking a mid-drive Bafang on a burly full-suspension frame for some serious trail riding. It got me wondering, especially for those of you who've done custom builds: how much do you factor in local eBike regulations when choosing components like motor wattage or top speed? Are there specific things you look out for to make sure your awesome custom creation stays street (or trail) legal, or do you mostly build what you want and then figure out the legalities? Keen to hear your experiences!