Hi Kumar28: Thank you very much for joining the Intel® Processors communities. We will be more than glad to assist you with the information you requested.
For your first question, on the link below you will find the list of boards that are fully compatible with each processor:
Intel® Core™ i7-7700 Processor:
Intel® Core™ i7-6800K Processor:
In regard to your second question, since Intel® does not manufactured graphics cards, unfortunately there is not a document available to confirm which video card will be fully compatible with our boards. In this case, if you are going to purchase a video card then what we recommend to do is a BIOS update to the latest version depending on the board you will be using.
Any further questions, please let me know.