I thought about this again: you don’t really know what you want, and you want to self build? Whatever you buy won’t be spot on because you don’t know what you want until you start riding.
Buy a cheap second hand frame from here (I’d say a steel hardtail for first go), build it, ride it, and you’ll soon have a better idea of what you really want. Don’t overpay on frame/parts, and they’ll hold most of their value if you decide to turn them over.
People on here will help you if you’re stuck. If you self build you’ll sever the chain with the bike shop: use them when you want to not because you have to. And (eventually … but the journey will be fun) you’ll get just the bike you want.