The fundamentals of boating at the same.
safety at sea
These are all things that are the same REGARDLESS of vessel size.
When you get a larger boat, it handles differently, docks differently, has different windage, has less clearance where you previously had clearance, has different more unique "stuff" on board.
Nothing you learn outside of actually being on a larger boat is going to prepare you for being on a larger boat.
As above, I'd get yourself onto a large boat; at the helm. I promise that after just a couple of hours, you'll have the confidence to put your doubt about "size" to rest.
Good luck, keep us updated.
If you want to have a full on crash course, come on down to New Zealand and I'll let you take me out on the big boat.
If your boating experience is minimal, just ensure you have thrusters at both end with enough grunt - and you'll find yourself comfortable in any situation. ;P