What I’m unclear on is where the project files actually reside (and the file/folder structure) and how to access them?
As you have mentioned, these files reside on the server itself. If you connect to your server via Remote Desktop, you can see the files under D:\sitesroot
folder (actual name of the folder can be found by launching IIS Manager on that server).
Having said that, it is not recommended to make changes to the files directly on the server. This is because if your server goes bad for any reason, Microsoft will provision a new server for you and it takes the code from the package file when you last deployed your application. This the changes you have made on that server will be lost.
Regarding your other question about having somebody focus on front-end development, I'm pretty sure you don't want him to working on production server directly. I'm assuming you have a centralized code repository somewhere where everybody checks in their code and then you build stuff and then deploy it.