Nice work, I modified the source code a bit for my needs.
Could you implement a fee system?
For example: User A wan'ts to make a TX to user B,
the admin (user C) get's 5% of the sendet amount.
Yes Fee system would be quite easy to implement. Feel free to create a pull request with configuration or create an Issue on the github repo.
I am interested to know what is the use case of actually sending fee to admin user in each transaction vs just cutting 5% off the send amounts. Admin user can withdraw anytime as anyway he is having complete access to wallet. Note that if you create extra send output for each payment you are increasing the tx size which would result in higher tx fee as well.