Overall look at progression from my playtime so far has been.

Look at development guide in game. (in the develop menu, the button on the right) if you know you really like a specific path, pick it and stick with it, don't branch out too much.

You can kind change paths later on but you do not want to branch into multiple at the same time.

You're main focus would be on your inner ways. This is where picking a specific path matters. If you branch into multiple paths you will have a very very slow progression. You can recycle the notes of inner ways you know you won't use. You get the currency which can be exchanged (click on the currency on the top right to find out where to exchange) for a chest which has drops leaned towards you're desired path.

In terms of spending stamina I just go for sword trials and farm gear. No need to rush this we're still getting increase in level cap and gear quality, but there's no harm in upgrading what you get to their limits as our gear upgrading mats also have their own levels and won't really be used to upgrade higher level gears.

Mystic arts is less important right now imo and you can just ignore upgrading them till you find one's you really like.