Mixing mushroom-potato-carrot soup and warming later (Should I?) I've got what is probably a pretty basic question - but this is the first thing I've tried to prepare in my life that didn't involve boiling noodles and adding cheese afterwords.

I'm looking at baking chicken breast in foil packets with cream of mushroom, carrots, potatoes etc etc. The thing is I'm only cooking for two people, so If I follow the proportions on my recipe I'm gonna have a lot left over, so I thought I'd make the leftover mushroom/spud/carrot concoction into a soup (possibly by adding some cream of chicken to thicken it up). This unfortunately adds a whole level of work to what I'm doing and given the fact that I don't want to start heating until my girlfriend is on her way over (which is somewhat unpredictable time-wise) but want it to be ready when she gets here (20 minutes or so) I'm wondering if I can prepare some of the stuff ahead of time.

I don't see any reason I can't cut the fat off the chicken or wash/peal/dice the veggies, but will the veggies get soggy or loose texture if I mix them in with the cream of mushroom up to an hour before I start heating it? I assume if I were to do this, it would be ok to refrigerate? Thanks so much for your help. If something I'm spouting sounds like utter nonsense or would taste terrible, please feel free to let me know! =)
You're fine making those packets well in advance. You could even put them together the night before and leave them in the refrigerator until you're ready to bake (expect them to take five minutes longer to cook). The only possible negative to doing it that way is that the potatoes could get a little brown. You can keep that from happening too badly by making sure that they are completely covered by a thin coating of the soup mixture. 

You don't want to serve soup made out of the same ingredients as your entree. That recipe is totally scalable, meaning you don't have to make any more than you will actually eat. At worst you're going to have some of the can of soup and part of a potato left over. 

I wish the recipe described the making of the foil packets a little better. If you're at all unsure about how to fold those, come back and ask. We'll help you out.

BTW, that begs for a green salad to go with it. You could put a salad together a few hours before your girlfriend is expected and keep it in the fridge. Just don't add the dressing or any croutons until you're ready to serve.