If you're not using a responsive system like Bootstrap or Foundation, you'll also have to decide whether you want to create the mobile version first and work up, or the desktop version first and work down.
You'll see arguments that you should always do the former, but I think it depends on your users. For example, if your site is full of stuff that won't work well on a phone (e.g., the MODX manager), most users will be using at least a notebook, and more likely a desktop, for most of their work. In that case, I'd start with the desktop version. Not everyone would agree.
Thanks very much for clarifying it can be done. And pretty quickly. I will be in touch if we feel we need more quotes. Thank you again.