cloning large git repo and setting up git repo from another domain

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Hi experts here

I started using github for project management.
1. how do i create a git repo using files from my online hosting account(like say files located in my hosting for sub domain site http://mysite.maindomain.com) so that i work with that git repo by cloning it in my local hard disk as this is the way working with git is done.so changes in those files will reflect in my site http://mysite.maindomain.com.

2. also for one of the project, online git repo size is approximately 1GB.if i try to clone that git repo in my local disk how much time it can take and what possible errors can come up?