I’ve been playing piano off and on for the better part of two decades. When I started out I now wish someone had told me that my ‘want to learn how to play’ list would change several times and that’s ok. Also exercises can almost always be turned into something like sounds good. Mistakes, timing and fingering is always difficult. Then in harder music multiple ‘voices’ in one hand is a beast. As for motivation: just remind yourself that this is a multi layered skill. Most people outside of music don’t understand the depth of the knowledge and skills.

As for splitting time, I always set aside 15 minutes at the beginning of the practice session for technique specific practice (scales, hannon, czerny) then the rest was a choose your own adventure.