I think an electric linear drive would make more sense on a 27’ boat. You need a good mounting point and the tiller arm to mount on the rudder shaft, but other than that, the wiring and computer are pretty simple. I upgraded to a Raymarine ST6000 wheel pilot last year on my 32 foot, 10,250# displacement O’Day 322.
I can replace the wheel drive with a linear drive in the future and sill use the course computer and compass. I have a rudder sensor mounted, and the wiring for a linear drive isn’t much more difficult than wiring the rudder sensor.
And I think you will find that a hydraulic unit will cost a lot more.
They both need power to operate, so a hydraulic unit isn’t going to help conserve battery power (not sure about the power consumption between the linear drive and the hydraulic pump…).
On edit, I see you titled this Hunter 320…so maybe that is the boat you are going to add the AP to…not the Pearson 27 in your avatar. But my comments work for either boat.
Greg