I've seen the linkages passing through the hulls for steering, and I think a better way to do that would be hydraulics. There are several off-the-shelf hydraulic positioners available for just that kind of application.
The system doesn't use a pump, but basically uses a steering wheel pushing a piston, like a two way master cylinder, piped to an exterior two-way cylinder connected mechanically to the rudder. Very low tech, and not prone to leaks.
As for the buoy release, I am building one for my sub that is really just a tube and ball valve inside the sub.
When I open the ball valve, the tube fills with water, and the buoy floats out and up. The buoy is connected to the bottom of the tube with a small stainless cable spooled on a pin.
The 3'' valve isn't cheap, but the rest is. I will be able to see the buoy release through the window, to verify that it has deployed.
Additionally, I expect to be able to use the same tube to jettison excess air or accumulated condensate water by opening the valve just enough to release the whatever, but not enough to release the buoy, and pump the air or water into the tube.
No moving parts spinning in a through-hull, just a big ball valve.
Frank D.