HVAC, heater core removal?

You can just lower the steering column to get it out of the way. It does not look like you will need to vacuum down the AC system so that part is good, here is how to change out the heater core, start by draining he cooling system and disconnect the battery. Check out the images (below). Let us know if you need anything else.

So I don't need to take the steering wheel off, just unloosen the brackets and let the steering column hang on the seat. What about the pinch bolt at bottom, it should be okay?

You should be okay, but I would support the column as too not stress the connection at the pinch bolt.