Garden consultant seeks software for invoicing and accounting

I am a freelance service provider in garden consulting and design and am looking for software for invoicing and accounting.

I have the following requirements for the software:

• Customer database
• Invoicing
• Online banking access
• No double-entry bookkeeping, only cash basis accounting
• Compliant with the principles of proper management and storage of books, records, and documents in electronic form
• Preferably Linux-compatible (Debian Linux), if necessary MS Windows 7-compatible (in this case, a Virtualbox with Win7 would be installed separately)
• If necessary, cloud software (ideally, this can be installed on my own web space)
• Cost-effective

One software workstation is planned.