I usually just browse and read the forums, but I saw your post and wanted to help. There's a lot of great content on youtube, but stick with GarageBand for as long as you can...master it as best you can..then you can upgrade to Logic Pro X and do even more. But don't buy that right away because you will be even more overwhelmed.
I was like you just a few years ago. Played guitar..bought a MacBook, saw GarageBand and thought hey, why not try this out. Fast forward a few years and I have recorded an album and several songwriting demos and still continue to fool around creatively with it. Usually just to come up with quick demos that I can later fool around with in Logic.
I learned as much as I could about GarageBand before I went on to buy Logic Pro and don't regret it. Logic Pro has almost the same interface and tools...but has more professional features..but they won't help you necessarily be more creative.
I'll give you a direct link to someone I found about a few months ago on youtube that I think is terrific...his channel name is garagebandandbeyond...you can find it here...
https://www.youtube.com/user/GaragebandandBeyond
This guy is a multi-instrumentalist and he is a great teacher of GarageBand. He does gear reviews on monitors, microphones etc. but he also does great tutorials on how to use GarageBand like a pro. He also records and posts his own creations and music videos to show you what GarageBand is capable of.
I know he doesn't have like 100,000 views per video, but don't let that influence you because he posts like 2-3 videos a week and they are either really informative of GarageBand or a great creative demonstration of what's possible with GarageBand.
Anyways, you say you are classical trained and are lacking creatively. Don't worry. Again, I was in the same boat. Everything I recorded for the first little while was not good because I was inhibited creatively and was just learning how to get my ideas out. I didn't like hearing myself played back. It felt weird. But with some time and patience you will be able to do a lot with it. I think especially because you are a piano player, you will benefit from learning GarageBand. There are so many synthesizers out there. I don't know what generation you were born, but I'm a millennial and we love EDM music. I wish I had learned piano first because there's so much you can do recording yourself in real time with GarageBand.
Anyways..if that was too long just take away these points from my post...
-don't buy logic until you master GarageBand
-consider yourself lucky you are a piano player
-don't worry about your creativity..it will come in time especially with GarageBand
-look up GarageBand and beyond channel on youtube
My hand is sore from all this typing. This is why I usually lurk lol...
All the best.
[doublepost=1549276759][/doublepost]Here's a direct link to his how to record and mix like a pro...
Also I forgot to mention how good the official apple documentation is for GarageBand. It's really clearly written and always updated when they release new updates for the software. You can find it in the iBooks store or online
https://help.apple.com/garageband/mac/10.2/
Another great resource if you prefer video and don't mind paying like 10-15 bucks is udemy. I used this site a lot for learning more advanced features and concepts for DAWs(digital audio workstation) like garageband
https://www.udemy.com/courses/search/?src=ukw&q=GarageBand