Set it where you are most comfortable as that is why you have it.  A good idea is to update the thermostat to a programmable version that will run the A/C mostly when you are home and according to your schedule as well as at the desire temperatures.  It isn't necessarily recommended to shut off the A/C on warmer days when you are not there as it will have to struggle to catch up when you turn it back on.  This would be due to the warmer air in the home and the storage of heat in the walls, ceilings, floors etc in your home.

Oftentimes the attic is the place to start.  Make sure you have plenty of ventilation, both intake and exhaust.  Check the soffit cavity to make sure you it isn't clogged with insulation.  There are formulas for Square foot of attic in relation to ventilation.  If you have a vapor barrier in the ceilling a ration of 1:300 sf is ok, otherwise about 1:150 is the rule. Second, check the insulation.  All air escaping into the attic should be sealed using spray foam or other sealants. Next, depending on your geographic location, make sure you have plenty of insulation in the attic.  Finally, something as simple as installing blinds over windows can be an economical solution to saving on energy costs.  As recommended in some of the other answers, an energy audit or getting advice from any number of qualified professionals that are willing to visit your home is the best place to start.

Yes, they absolutely can be painted.  Go to your local Home Depot, Sherwin Williams or Lowes for advice and color selection.  It is best to remove the shutters first.  This will probably make the job easier and you won't have to paint on a ladder if the shutters are located over one story high.  Next, check on the anchoring system.  If they are connected into say, a vinyl siding, you will probably wreck the plastic, ring shanked, fasteners.  You can get these at the above box stores as you will need new ones to re-attach the shutters when you are done painting them.  If the shutters are over brick, the removal process is a bit easier as you can simply remove the screws.  If this is the case, check the mortar anchors to make sure they are still well intact.  Most of all, have fun.  These projects can be fun and rewarding if you start with a good plan.

It sounds like the back room of the house was really cold during the winter. One thing to consider is to insulate your house from the outside before using either type of siding.  This can be done by the right contractor.  Next, what type of siding do the neighbors have?  While you want your home to be unique, to a point, this is something to consider.  Hardie does give you a more traditional look and will allow you to change the color scheme of your home at a later point if you chooose to do so.  While vinyl siding can also be an excellent choice, I would stay away from insulation backed products.  To guarantee a good vapor barrier Fanfold insulation board is the better choice.  It comes in different thicknesses and is installed before the siding.  This allows the contractor to tape the seams and avoid gaps in the insulation.  There are two things to consider using insulation board.  They typically give you minimum R value for insulation versus removing the exteror cladding and insulating between the wall studs.  Second, using a very thick exterior insuation board will probably require trimming out all wiindows and doors.  Putting on thick insulation board will, in effect, cause the siding to significantly stick past all openings and may not give you a look that you like.  Please visit http://www.croixco.com/ for more ideas and possible answers to your questions. We would also be willing to visit your home to give you some ideas and solutions.  Call 847.895.8125

Will the workers be employees? or subcontractors? These people may be working in your home, maybe while you are at work.  Have they had background checks?  While most companies are required to have Liability insurance to get and kee their license, do they have Workers' Compensation insurance in the event a worker gets hurt?  How long will the project take?  Will they be disturbing Lead paint or asbestos?  If so, make sure they are certified to deal with these materials.

Check seals on doors & windows.  Replace single pane windows with newer products.  Check the attic for insulation.  Loose fill, blown in insulation is the best.  Make sure to seal any spots where air is escaping INTO the attic first.  Also make sure your attic has both adequate intake AND exhaust ventilation.  Make sure not to clog the airflow from the soffit area and the attic space by using Baffles as seen in the picture.  Check out YouTube for other great suggestions. 

We always suggest clients spend some time on Pinterest first to narrow down their ideas since there are so many options available.  You don't want to discover what your budget will allow by spending endless hours confusing material selection with company selection.  Next, research online and find 3 good companies to interview, narrowing your search down to one.  It is an involved process so you have to have chemistry with the person you work with.  Make sure they will be available throughout the process, not just for the sale.  Consider all components to the kitchen: appliances, cabinetry, heating sources-gas, electric etc, flooring, flow & lighting.