WalnutPixie's post is great, well thought out advice. That would be the advice I would give also, on the forum or with real life clients. As a new owner/rider it is a great benefit to start on a horse that has the knowledge already. That gives you opportunity to know how the finished product should work, gain skills safely and build confidence. Then someday revisit the idea of starting from the ground up. It is a rewarding thing to do but as said already, it isn't always an easy row to hoe.
From your post, it seems you have the want to and willingness to learn. That is a tremendous asset when venturing into horses.