What happens to my character? Will I be able to then reinstall it and play the other side of the story?

If you uninstall DG on your computer, anything that deals with that DLC will vanish. If you reinstall it later on, you will have to complete everything over again. So yes you would be able to play the same character through the other side of the story that way.

How does one even uninstall this?

You technically don't even have to uninstall it. When you first start Skyrim, instead of hitting play go to Datafiles and uncheck the Dawnguard box and there you go.

I think you then load the character and save, exit skyrim, reselect the dawnguard box and then resume and you should be able to start over.

Tried that but it causes Skyrim to crash right before the main menu fully loads.

Disabled mods and I was able to save the game and have since reloaded with dawnguard reinstalled but I'm still a vampire so I'll have to take care of that. Unfortunately I am now unable to enter first person view.

I now run super super slow and it seems like time has stopped for everybody else in the game.

*EDIT*
I fixed this specific issue by loading an earlier save. Still unable to enter first person.