Need help with a newly installed theme on the site

So I brought the theme from themeforest, but unfortunately did not check that the author is known for delayed support which is kinda sad..and im stuck with few things which I need a solution for and cant rely on the author for it..so was wondering if you guys can help me out here...

1) The theme says, it has Visual Composer, but when i try editing the frontend it just goes in an endless loading..and im unable to edit the page..

2) There is a setting on pages i think it uses (Meta Boxes) to set custom header for the page, but the funny part is , the media library pops up but when i choose an image and click select it does not get selected.

Can you guys please help me out here? Ive enabled the support i guess.