What should I expect (cost/process/timeline) for hiring a designer to design my entire social media website?

I'm not terrible at design but when I think of designing/programming the frontend + backend/maintaining cloud infrastructure for a social media website I have, I just feel incredibly deflated by all the work that will go into it.

This year, I've decided to save money and put both time and money into my idea. I've never worked from a blank page though -- all the companies I've ever worked there was always some basis to work from.

I was on Behance and I really love this design for a social media site -- https://www.behance.net/gallery/102495869/Social-Media-Manager-Web-Dashboard-UIUX

Off-color side bar that converts to a hamburger button in mobile, notification + accounts in the upper right corner -- modern and clean. I imagine having some list views, detail views, icons and assets to work with that I could extend myself when creating new features and new pages.

I don't know how this process would be. What should I expect to pay? How would I set the initial delivery of templates? Would I have an ongoing relationship with the designer -- a retainer of sorts? Is there a template for the minimum amount of pages I should have designed? How do I draw up the contract for that?

Hell, where would I even look for good designers who want to be hired?

Thanks in advance.