Heating the basement

That certainly is much the simplest way to do it. If all the baseboard is going to be below the water level in the boiler, all you need to do is find a convenient tap on the boiler below the water line, pipe from that to a pump, then the baseboards, then back to a wet return somewhere. The control can be just a thermostat to turn on the pump -- although you can get fancy and add an aquastat to turn on the boiler to make sure it's hot. Doesn't take much of a pump.

Yes, if you heat blow the water line , you don't need a heat exchanger to pressurize the column of water . Just to note circulators get eating up with solids left behind . Maintain and repair any steam leaks