I work as an independent contractor providing web development services per your requirements. Meaning, I'm familiar with a designer giving me a .psd (or other format) and then turning that into real responsive code / in a CMS.
I'm mainly familiar with HubSpot and WordPress. Some sites I've worked on are roku (yes, that Roku...), habitat for humanity, kasasa, inova payroll (wordpress), thoughtrace (formerly agile upstream) and some others. I'm familiar with Wagtail (Django CMS) and even building my own as a current personal project. So, you'll see I'm no stranger to web development using things exactly like SquareSpace. It's just a different platform.
So, if you're willing to take a chance on a developer that hasn't used SquareSpace exactly (but identical development on other platforms....) I'm happy to work with you and provide professional grade websites on an ongoing basis.
QUOTE: This is impossible to say without a design doc. All of those elements are listed, but the design doc could be extremely convoluted. This is just unrealistic to attempt to give. However, with full materials from the designer sites can usually be turned around within a week dependent on their complexity.