As an experienced cyclist with a lot of tandem experience: you are way over thinking this whole thing.
Assuming both of you are adults and not complete klutzes, you'll have it figured out well enough in a few minutes of trial and error. If you're not both adults, you'll still figure out within a few extra minutes.
Getting to be real slick starting and stopping instantly takes awhile to develop as a team, but just getting going is pretty easy. As andy256 said, the captain can ride around on it for 30 seconds to get a feel for it, then add the stoker.
Two of your comments to address:
- The stoker can't just maintain "some" cadence, they have to maintain exactly the same cadence as the captain, unless the tandem is very fancy. Normally, both cranks are always in sync. It will be up to the team to manage it between themselves what the ideal cadence is.
- The stoker should not maintain any balance per se. This is one thing some teams struggle with early on. The stoker should always be sitting 'upright', in line with the plane of the bike. The stoker should not lean to help steer. All steering is to be done by the captain exclusively. Attempts to steer by the stoker leaning can make it difficult for the captain to control the bike and maintain balance.
Also, while the captain is in control, the stoker is in command. The stoker decides how fast the team goes, where it goes, when it stops for a snack or to take a picture of a puppy, etc. The stoker has no control of the bicycle whatsoever, so by the stoker having control of the trip, will help make everything go much smoother.
Read http://sheldonbrown.com/tandem.html for instructions on how to get started, or don't, it's really not terribly complicated. And have fun, it's a blast.
Wherever your relationship is going, your tandem will get you there faster.