When piecing I use a Clover mini-iron to press my seams; only turn the big iron on when absolutely necessary. I replaced my incandescent light bulbs with florescent (curly Q) bulbs. I didn't have to do it, but you might add foam insulation panels (about $7 each) inside your room against the outside walls. They are for insulation, but they make a great design wall/pin board/whatever board. Each sheet is 4x8 ft and you can install cabinets or shelves on top of them. That will accomplish the same thing as your AC guy is telling you to do, but won't break the bank.
The foam panel I bought for my design wall is white and came from Lowes.