Yes you can repeatedly write sessions onto a multi-session CD/DVD until it is full. Every time you add a session however, some of the capacity of the disc is used for the session itself in addition to the capacity used for new data, so you won't be able to fit as much data on the disc compared to if you write everything at once in a single session.
I wouldn't use a CD-RW for years putting new data on it - CD-RW are not as durable as CD-R over time.
InCD doesn't support using recordable (non-rewriteable) media, so InCD does not come into play when writing multi-session CD-Rs (* but see below).
If you're using CD-RW you can choose to EITHER write a multi-session disc with Nero Burning ROM, Nero Express or another burning progtam, OR you can choose to format the disc with InCD and use it as a giant floppy-disk. I would recommend against using InCD for important backups however, as many people including myself have experienced a loss of data this way. Use multi-session writing instead.
*) InCD and other "packet writing" applications may interfere with some burning programs, so there's a chance you will experience an incompatibility problem.