I was wondering if sc2 will have the same balance as sc. Such as ums. WIll it still be playable?

Not really sure what you mean here.
Will it have the same game types such as UMS? You bet. Supposedly we get to even use some SC1 units in the map editor for ums.
Will you be able to port SC1 maps to SC2? 99.999% chance not.

IP, I think he means the second one, and no, I don't think so, I believe that even the old units will be changed to make them fit with the newer ones, and certain units now have special abilities that make them better than they used to be.

No, old units will probably be exactly the same as the original. Atleast the ones that aren't actually in SC2.