Wireframing problems

I asked a lot question before but I decided to ask them simply.

1- Which screen size I need to wireframe for, Is it matter page size? 2- Do I have to wireframe for 3 devices (mobile, tablet, desktop) 3- If the second question is yes, How must be the page size of each devices in the wireframe program (in pixel)? 4- Do I have to use grid system when I designing for these 3 devices? 5- If fourth question is yes, How many column does a mobile phone use? I had read 1 column in an article.

6- If I need to use grid system, Can I download it from somewhere? 7- Which is the role of the wireframe in the next steps? 8- Once I completed the wireframe, what I need to do (visual designing etc?) 9- What is the relation between a wireframe and responsive design? 10- What are your ways to make a responsive web application from scratch to finish (The most important question)?

These are all questions that came in my mind. If any further questions come in my mind I will add them at the end of the list. Thanks everyone...