Is the universe always expanding
It will always expand (probably).

The mass and energy in the universe curves space, and it seems that there is exactly the right amount of mass and energy to keep the universe expanding forever. 

Had you asked this question 20 years ago the answer would have been "we don't know". Recent discoveries of "Dark Energy" suggest that the expansion of the universe is not slowing down, but speeding up. This would mean that the universe is destined to expand forever, at a faster and faster rate.

The notion that there will be a "Big Crunch" followed by another "Big Bang" was seriously considered by multiple scientists: among them Willem de Sitter and George Gamow. There are problems with this hypothesis: It is not well supported by observations of the rate of expansion. Moreover, there would need to be way to reduce the entropy of the big crush, as entropy can only increase. And moreover any "pre-big bang state" may be hidden behind the singularity at the start of the (current) universe and so fundamentally hidden from us.