If you want to set up a business in Germany, you will need to choose a legal structure for it. In your business plan, you should give reasons for your choice. Additional information on legal structures is available on this portal under “Startup types: Ways of setting up your business”.
Checklist for your business plan (English, German)
BMWi GründerZeiten no. 7: Businessplan (business plan)
Checklist for your financing plan
Things to bear in mind when planning your business finances (German, English)