First, its likely the unit proposed is 12,000 BTU heat and cool, not 1200 so its significantly larger capacity than your previous window unit. Most mini-splits are much more efficient than your window unit so energy savings will be in order, not to mention its a heat pump replacing strip heaters. 12k may be too large, 9000 units are available and cheaper. Also efficiency up to a SEER of 19 and they are VERY quiet. I would stick with a major brand unit, not a chinese import with no parts support. LG, Fujitsu, Mitsubishi, Panasonic and Sanyo. Unfortunatly the american brands have not really entered this market yet, they are much more popular overseas.

Yes, they can be had in cooling-only. I think that the heat pumps are a little more expensive than cooling only, but not much. I can not comment on the relative efficiency. The heat pumps are mechanically more complex so they have more failure modes. I have three multi outdoor units for my seven room house. The reversal valve crapped out on one of mine just before the one-year warranty date. (Note to you AC guys, it stuck in heat mode and would reverse if I tapped on the valve with the butt end of a screwdriver.) I do not think that is a big consideration, but you might want to discuss that. What is the advantage of heat pumps to you? Maybe a lot and maybe none. Do you heat with oil, gas or propane? You can compare your heating costs with your current fuel and electricity rates and decide if you want to heat with heat pumps in relatively mild, but cool, weather. There is a cut-off temp where they fail to perform well when it gets colder. You can zone your heat when you are using them, adding more economy, heating only the rooms are sitting in to comfortable temp and leaving your main t-stat set lower. (This gets a little complicated if the t-stat is in a room that you are heating with the mini split.) Tip: when heating with high wall or ceiling units, you will probably want to turn up the blower manually higher than its programmed speed to keep the heat near the floor and not accumulate near the ceiling. On the other hand, your ceiling paddle fan will take care of this as well if you have them. One thing you might want to keep in mind. I can say that the Mitsu (and perhaps all brand) multi are less efficient than the 1:1 units and they do not do as well as the single units with heating at low temperatures. For the former, I think it stems from the fact that the compressors only throttle back to a certain percentage of max. For example, a single unit might be rated at 9000 BTU. If you only need a little cooling, and assume that they throttle back to 10%, you can efficiently get 900 btu out of them running constantly with no on/off. Your tri unit is probably 22,000 btu and can throttle back to 2200 btu with the same assumption so your compressor will be flicking on and off more often which yields poorer humidity control and not as even cooling. Please, keep in mind the relative nature of my comments. These things all work really well compared to window units and compared to central forced air. Be sure to consider all of your alternatives for the installation. In addition to wall-hung, you can have floor mounted, short ducts to hidden units and ceiling-mounted. That all costs more though. You have probably seen the pictures of installations with the plumbing straight through the walls to the outside of the house. Mine are run inside the walls to underneath the house. Again it might cost you a little more, but talk about it with your contractor. You should look at the MItsubishi, Sanyo, Toshiba and perhaps, other web sites to get some more information about their equipment alternatives. Your contractor should be willing to discuss all of this at length with you since you are making a big investment. I hope they can evaluate your cut off point for economical heating with the heat pumps vs. your hydronic heat. They should be able to estimate for cooling only vs heat pumps. The price difference might be trivial, however.

Ductless heat pumps are often relatively limited in the space they can heat and it is not cost effective to add one to every room. A ductless heat pump mounted in the living room will rarely provide enough heat to auxiliary rooms that are farther away, such as bathrooms, bedrooms and kitchens. I have heard about infrared heating products are a great compliment to ductless heat pumps.

If window units will keep you comfortable, then mini splits will as well, but with less noise and higher efficiency. Although window units are getting better all the time, mini splits will probably do better humidity control too. Mini splits vs. ducted systems is more of a continuum than it used to be. There are mini split ducted units that can handle more than one room. The difference, I think, is that the static duct pressure is much lower so the design approach is totally different. In a well insulated and constructed home, heat and humidity move between rooms a lot faster than through the exterior walls. That's why zoning does little good in economy measure in that kind of home. It will help you with any uneven temperature problems. Complexity, as Austin pointed out, increases with the number of units so that is a negative. Keep in mind that with more than one compressor, you throttle back to a lower output than with one large one running three. That keeps you out of the cycling mode longer and keeps humidity under control better if you are not running all three units indoors. I've posted a lot about mini splits on this forum even some this week. Take a look.