Traveling to Azerbaijan

Hi! I'm gonna make a long trip to Europe and Asia in 2018, so I'm currently building my plan for the countries that I'm interested to visit. When it comes to Azerbaijan, I would like to ask you some questions:

• Which cities do you recommend me to go? Also: Which places in those cities do you recommend me to go?
• Also in those cities: Are there places or neighborhoods that you don't recommend me to go (for safety reasons, crime, etc)?
• Which national and natural parks do you recommend me to go?
• What's the most used transportation between the largest cities? How's the situation with Uber in your country?
• Do you often use cash or credit/debit card? (I usually use cards so I don't have to carry money with me at the hostels)
• Any other recommendations , safety issues or other advices that you would like to comment on?

Thanks a lot in advance!