ugh, i feel for you. first, read your lease very carefully. you will be required to give written notice (certified letter best for proof) to Landlord of the problems. clearly Landlord is aware by now of the problems, and is trying to fix the situation. (he probably can't find someone to come out sooner, thus the space heaters, but that's really his problem, not yours.) but if you haven't sent the letter already, you should now.
if you want to move out, carefully read your lease again. you are legally required to pay the full year's lease. so anything less will be a decision made by you and the Landlord.
your city or county may have a free Landlord-Tenant office to help with disputes. there may be specific local laws about withholding your rent payments (you may face an eviction record if not done properly), or allowances to let you repair the furnace and have the Landlord pay you back.
also, you might want to buy a cheap wall thermometer, and take photos of it with your phone (which will record the date/time) when the indoor temp goes below 65 degrees. finally, check your Renter's Insurance. good luck!!!