A light not working is so minor that it might not even be an issue pre-closing. And "cold upstairs?" If the heat was on when you walked through the house was it cold upstairs then?
Without reviewing your paperwork I can't say for certain, but I've never read a bank contract that accepted responsibility for so much as a burnt out light bulb. In most cases you have an inspection or due diligence period to investigate everything you can.
You may have more success with the builder if they are still around. The issues you mention don't sound too serious. Check the insulation upstairs and see if your furnace fan can be increased to push more heat throughout the house. A light fixture isn't too expensive, depending on what you choose.