To answer your question, "Yes", you can use CD Architect with Sound Forge 5, meaning they can be installed side-by-side with no conflicts. However, CD Architect will not dock with Sound Forge 5. This means you'll have to run two seperate versions of Sound Forge simultaneously, one for you editing (SF5), and one for CDA to dock to (SF4.5). Again, this will cause no conflicts.
I'm a bit confused at the wording of your second question. Are you asking if it's possible to record multiple tracks to CD with SF5? Yes and no. Yes, because you can write as many tracks to a CD as you wish until it's full since SF5 supports track-at-once burning. However, it does not support disc-at-once burninig, which is writing several tracks at once.