It is not uncommon at all for a boat to not have a main switch to kill all the power. My 2004 model year 24 foot Maxum did not come from the factory with a switch either.
Fuse boxes are usually found near/under the helm, and typically accessed by a small removable panel. Sounds like y'all have already found the one on your boat.
What else ya wanna know? Feel free to ask away.