Download Debian packages and dependencies on Windows?

I am working in a restricted environment. I have a Debian system (Jessie) with no internet connection. I want to download the packages and dependencies on a Windows machine (where I don't have admin privileges) and then install them on the Debian system (I have root access to the Debian system).

How can I download the packages? Can I download them using a browser?

Is it possible to download the whole repository as ISOs? If so, how big is it? Where can I find this information?

This for a project where I need to develop a driver.

I might need simple things like gcc or maybe some utility software. The problem is that the uncertainty is too high as to what I might need during the project. So I need a solution where I can either:

download any package anytime I want on a Windows machine and then install it on the Debian system, or
just download the complete repository on Windows and set it up as offline repository.
In any case, the download is possible only on a Windows Machine with no Admin privileges.