Question 1. even though you clone the homestead repository on D, virtualbox will create your virtual harddisk drive and other files on C. So you better have free space on C

Question 2. GIT and Composer are two different tools with different usage. You will need GIT and Ruby for Homestead to work

Question 3. 4GB is enough. Homestead runs on a very light version of ubuntu, which requires around 1-2GB. for nodejs to work on homestead you need at least 2GB

Question 4. No problem, You IIS server will server from your local environment while the Homestead environment will have it's own IP which you can state on your hosts file.