26 year old A/C? That is past its useful life. Plan for it to be replaced and either ask the seller to do it or have it reflected in the price. The good news is you'll have a much more energy efficient system. Same with the water heater. Replacing and moving the water heater should be under $2000. No idea on the flue pipe. Termites absolutely need to be taken care of and the seller is going to have to do that if it is you as the buyer or someone else. I would just want to know what they are doing and that it is adequate. My realtor steered us clear of stucco because in our market it is frequently done improperly and causes moisture/mold issues 10-15 years down the road. Even if you test for moisture now it can check out fine but cause issues down the road. I don't know enough in other markets though.