As for updates, the Level 1 and 2 packages are safe and have been approved by Clem for inclusion. The Level 3 packages are from Ubuntu, so you may wish to pick and choose what you actually need to update since there can sometimes be odd results.
Yes, please use mintUpdate for your updating. I know some people are used to updating everything via Synaptic, but that method can bring in major changes such as kernel updates and the like which can wreak havoc with some systems.
As for video drivers, I shall have to leave that for others who have that experience. I only use the provided open-source drivers. Good luck.