Bill & Lisa,
Following on John's and Karl's comments above, you will need a below decks autopilot because of the size of your boat. It is generally less expensive to use an electro mechanical piston autopilot vs a hydraulic one. The hydraulic units are more powerful (oz. for oz. - kw for kw), but I doubt you'd need to go there for what you're doing.
I think that the weight of the boat is not really as good a measure as the control surfaces efficiency (usually the rudder), the balance of the vessel (especially under sail), the sea states that you'll be sailing in, your battery and other electrical capacity and recharging system, and then weight, LWL, and so forth.
The "guidelines" that most manufacturers use is generally gives you a less expensive and underpowered system which is more prone to failure -- especially if you are really challenging the system under sail in a seaway and sailing with a lot of pressure. Sometimes, depending on the boat, it can even be a problem with motoring in tough seaways.
If your apparent wind and speed over water instruments are Garmin, I'd tend to go with that same manufacturer because the interface is less likely to be an issue. If you have Raymarine or one of the Simrad products for those instruments, I'd similarly go with them. The chart plotter will be sending information for purposes of GPS routes which is pretty generic.
I think that having an apparent wind function with a good autopilot really make a difference with shorthanding or on longer watches. There are differences in the quality of various manufacturers software and their ability to handle the impact of seaways, currents, variations in wind speed, the rudder efficiency, AND HOW YOU did or did not BALANCE the sails vs. the sea state & wind conditions.
I don't have any idea how efficient and powerful your rudder is, how you and your sails balance in the sailing conditions you're using them, and whether you really "get out there" in rough conditions and keep sailing. It's better to err on the side of over sizing, unless you have economic or electrical power constraints. In my "GUESS", that's one or two sizes up with electro mechanical for you. If you were going to be taking the boat to Bermuda or down to the Islands, then you might go up more, etc.
Usually you'd have a marine electronics firm install the autopilot and integrate the systems. The autopilot "piston" would likely connect to the steering quadrant on your rudder (unless Hunter has something odd).
The control head for the autopilot should be accessible from the helm; and, hopefully from the cockpit behind the dodger where you might be sheltered a bit, or trimming the sails. I think it a good idea to put multiple heads in so you can use the pilot to help you in situations that you might find yourself really appreciating the help while sailing the the boat or toughing it out in crappy weather or the unrelenting sun on a windless day.
If the Garmin unit provides for you to control the unit using the chart plotter at the helm, I would STILL HAVE AN INDEPENDENT stand-alone control head for the autopilot. I like redundant systems and controls.