I like what your trying to achieve here, I'm after something very similar to manage my clients.

I think taking 25% of any profits is more than acceptable given that most of these crypto late comers don't really know which coins to invest in, that expertise takes time and rightly so we should be cashing in on that knowledge by now.
I would suggest a negotiation feature to adjust profits per client and the ability to set dates and even back-track profit by selecting dates in the past.

The UI looks good, I'd be interested in taking a look at where your at now.

Exodus wallet im a big fan of because I know I have my private keys and their UI is enjoyable to use, I'd highly suggest a desktop application for Mac/pc that manages not only my portfolio but also my clients.
Also Exodus does backups and recovery and it would be a great feature for clients to be emailed their backups so that they know they can trust you, at any time they can recover their accounts should things go south with the relationship but only without the % fee set out in your application - so that they you know your getting paid.  Sounds ideal but would take some figuring out.