Need help for app development

Hello Friends

I am entering into Apps development. And I am new, so need to know some basics about it. I am using seattlecloud platform only.

1. How much to charge per app (for android and IOS) from offline client (from small business owners like Restaurant, Bar, Real Estate etc )
2. Places where I can find customers for the business
3. A list where I can submit my app for free??
4. Your suggestions too
5. Some app promotion methods

Thanks in advance.