Arduino Hardware Choices - Help Needed

However, I would like to purchase most of what I need up front.

I'm curious. Why would you want to buy most parts up front?

I find that, as I learn more, my ideas become more refined, my focus becomes clearer, and I may realise I can do much more with just a different selection of parts, or do everything I need with less.

Sorry if I am prying. That isn't my aim.