I am running pex tubing in a bathroom I am building in my basement. Can the pex run flush with the 2x4's or do I need some kind of spacer so it is not laying flat on the wood? Also what kind of bends can the tubing stand?

It would be better if you used some kind of clamps to anchor the tubing to the wood at intervals that will keep it from kitting the wood and making a noise. There are several different kinds, I like the kind that is a stand-off from the wood.

The pex can be bent to the point just before it starts to flatten out the arc and you sure don't want it to bend to the point of making a kink.