Completely agree with the above re: your inbox. I've gone through periods where my inbox is completely out of control and it materially effects my ability to get my head around and complete my work. So absolutely the first priority is to clear your inbox. I'd go further than suggested above and move the entire inbox into a temp project.
In my experience both when I've gotten out of control and when helping others - there will likely be actions for you in your inbox, but it is also likely that there won't be any that you'll actually end up doing (except if they go on your someday/maybe list) on emails going further back than 2-3 months.
So my suggestion:
1. Move your emails into 2 project folders, <= 3 months and > 3 months
2. Adopt good practices in terms of inbox zero straight away, so that your backlog is quarantined
3. Immediately scan your <= 3 month folder for any action items and add to your system
4. Do the rest of the GTD set up in terms of physical processing, mind sweep, etc, taking a similar quarantining approach if needed
5. Set a project for each of your two folders to process them per the GTD methodology
Do, or do not. There is no try.