Questions regarding games development

[kamikaza]

Hello! I am slowly getting into iOS game development. I don't code or design myself, working with freelancerfor this job mainly.. I have done very simple games before like puzzles.. And I want to make a 2d runner game.. So can anyone share their experience..

Is it better/easier to use Cocos2d for 2d games?

What kind of images are needed for game background? Keep in mind it's a simple endless game ..

What type of animation is needed for main character- he runs all the time, his hands, feets are moving. Should I use a .gif image for this?

Thanks for answering!