AdMob revenue analytics by country and app type. Who faced what to expect?

Question

Apple App Store

Hello.
Have a registered AdMob account.
The application with AdMob is planned to be made on PhoneGap.
1. Feels like: does it make sense to invest efforts and which application plan generates more revenue from AdMob advertising and in which countries?
2. If you have at least one application with AdMob: did you make 2 versions at once (free with ads and paid without ads) or only one with ads?
3. What do you think is the main criteria to consider when designing the interface of an app that contains AdMob ads?
4. What is the best strategy for promoting an app that contains AdMob ads?
5. What are the ways to distribute their applications, except for the office. Application stores (GooglePlay/AppleStore/WindowsPhone market) have you used and how effective is it?
In advance, Thank you all for your helpful advice and help.