Creating an app

I need a / client / financial management system for a freelancer. The details: 
1) The system should be based on Zoho, Ninox or another popular low code system. It will be used in the web and will be displayed in the browser. 2) All of my clients (around 60, with an upward trend) would be set up as team members and have their own page on which they are responsible for maintaining their personal data (address, telephone number, login data for websites, etc.). Each team member can of course only see/edit his own page. The login has to be protected, if a user loses his password, he has to have the ability of receiving a new one by email. 3) Invoices are filled with the master data from this client list (see point two) and output as a PDF. 4) The tax is also prepared in the tool: A script logs into the bank and automatically imports all data from the account statements. Further information is added 
a) automatically (booking number) b) manually. (intended use, my personal comment, PDF upload of invoices, percentage of TVA, ..) c) automatically calculated (net amount after choosing the percentage of TVA from a select box.) 5) Export of the tax data: a) Only a simple export function is needed, the data should be exported to excel. b) The export of all data (including attached PDFs of the invoices ) to my tax consultant. Important: 
1) The app and the software on which it is based must comply with the GDPR 2) Please note that I work in Germany. Therefore my bank is German. You need to know how to login into German bank accounts. 3) Refers to point 5b (see above): After exporting the data to my tax consultant she will use DATEV ([login to view URL]) to work on it. Therefore the exported file has to be compatible to DATEV. Pleas do not bid o that point if you are not sure about it. 4) Please provide me with information about your qualifications. Since we talk about sensible data, you will have to prove that you can do that job. Please also inform me, if there is any kind of liability or guarantee if problems arise later.