Hey Kasey54:
I think you are right on track by thinking of combining conventional copper with newer pex.
Check out the copper x pex stub out at pic. below.
You can also presolder a bunch of these up yourself using 1/2" copper pipe (type L), 1/2" pex x 1/2" copper straight adapters and 1/2" copper caps and elbows.
The big advantages to this are that:
1) pex does not like to make short 90 degree turns easily.
2) copper can be clipped/hung rigidly and stays rigid and aligned
3) can use conventional finish fitttings for copper (sweat or compression).
You can do the same for heat pipes, too. This way you have transitioned to copper pipe out of wall and can easily hook up copper baseboard without having to transition at each connection at finish.
And FOSTAPEX (type in at google bar) or similar pex pipe is way to go on runs for heat...you will love this stuff!!!
Anyway..that is my thoughts..Good kuck and keep us posted as you have been...

Mark