When do you plan on using it again? It would be best if you could get it completely dry inside the water jacket but that may not be possible. I doubt it will rust much during the winter since the residual water will be frozen.
If you are going to use it again next year, maybe just wait till the temps are getting down into the 20 and drain it, then refill it in the spring and add treatment as soon as there in no danger of freezing.
If it will be longer till it is used again, I would just drain it now. Also, I would flush it out so there isn't any sludge in the bottom holding moisture.
The lines you will want to fill with RV antifreeze. Either fill the pump full of RV antifreeze and make sure it comes out the bleeder screw or take it off and store in a heating building.
If you take the pump off, I would try getting all the water out of it. If it just dries up in the pump, it will leave all the minerals behind and might seize it up. Maybe take it apart and clean and dry the rotor and rest of the insides. If you have a Broeder pump, maybe just buy a new cartridge for it instead, especially if yours is a few years old.
As far as the rest of the boiler, just the recommended summer maintenance should be fine.