Seems I am late to the show, but I will comment anyway. :-)
1/2. I personally use a repository other than those provided by either site because I thought being in control of my repository is a better thing than relying on others. If I were to start a repository from scratch I would use git, and if I could not host it myself would use github as the origin (main repository).
3. Most things for git you can ignore until years later. You really only need to know how to create a repository, and check things in and out. Learning how to create and merge branches you will find will be extremely useful, as one of the main reasons to use git is because its branching system is extremely powerful. When you want to experiment with a new feature you can easily make a new branch and work on that without worry as the cost of creating a new branch is minimal and so much better than Subversion. As mentioned by others, you can actually have multiple sites hold your git repositories very easily, so your origin can be on github, but you can "mirror" that onto any other site that hosts git repositories, and you can conveniently name those repositories like Rainrider does to easily understand where you are pushing/pulling changes. Collaboration with other users using git is quite simple as well, and you can directly pull from their repositories to incorporate their changes. However, this is not something you normally really need to worry about when just starting. The most important thing is to come up with ways you go about tasks, and keep that simple, but powerful. One of my favorite tutorials on this is:
http://nvie.com/posts/a-successful-git-branching-model/ and hopefully you find that helps a lot to make things clearer.
4/5. I create the zip files myself and manually load them to both sites. I have my master documentation created with the specific markups for both sites as well. Basically I use a Mac and my development environment (Xcode) is set up to allow me to generate the files I need to upload automatically (as long as I remember to update the TOC files, etc.), and once they are generated I go to each website and update the changes. I do use curse's localization and when there are updates there I export the information and integrate it into my source code, but other than that I do not rely on any of the sites' automatic package generation capabilities. I also only put the release products on those sites and maintain prereleases on my own site.