I saw online that the G-force was 5G- is this true? Could it be dangerous?

Not true.

0 - 60 in 2.8 seconds, and then right into the loop, which is where the "up to 5g's" occur. It is a rollercoaster, it has all of the necessary health advisories to try and shield Disney from lawsuits (or at least, make it easier for them to fight the lawsuits when they come.) Normal healthy people should have no health problems with this ride. Millions ride it every year (since it's opening in 1999), so it's a safe attraction. Enjoy the ride, love it, and rock out!!!

Yes 5Gs. Health advisories can be found on the Disney World website.