What is that main difference between the original and the expansion besides 1 new act and 1 new character. I plan on playing today and buying the expansion this weekend.

Any level or skill differences?

Level extension, paragon, rifts/GRs, the works~

Maybe I will start another barb today and mess around until the weekend when I can pick up the expansion

So you can only get to 60 on classic and then 70 on expansion?

Yes