Hi 1919 house buddy! Mine was converted to forced air at some point, no idea what original heat source was.
Kitchen: My first thought is that you should investigate turning off the heat just in there and see what impact that has. If you can, you may get enough heat from the boiler/oven to be adequate. You do need to be careful not to disturb the overall function/flow of the system though, as that could damage the boiler or introduce other temperature variations.
Attic: um, it's an attic. Hot in summer, cold in winter. This is a universal truth. Hot air rises. A portable A/C unit will help in the summer. What's the temperature in winter? Heat the people, not the space. Blankets, small space heater, better clothing. We had thousands of years before central heat, look to that for ideas. Make sure your insulation is up to snuff as well.
Basement: The humidity and cooler temp is typical. They're at least partially below ground after all. A dehumidifier is a good idea, though 60% seems too high to me. You're going to encourage mold/mildew with that level. Do you need a larger one, or to have that one run longer? Additional airflow in the basement itself may also help. This should subside in winter.
I would not reopen old vents. You don't know what you might be getting into there. The problem with pulling air from basements/wall cavities into living spaces can be serious. Particularly if you're pulling additional humidity into the main house you could end up with moisture problems.