I have a baseboard heat system with natural gas. We had to cut a radiator out of a kitchen so we could tile the floor. Everything seems to have gone well and the heater is working after refilling it with water. We put a hose on the drain and introduced new water into the system. We turn all thermostats (4 different zones) and turned up one thermostat at a time and left the other 3 off while draining and introducing new water. A lot of air came out and after all was said and done no more air was coming out of any zone. We also opened a bleed cap on one of the pipes in the basement and water was coming out, no air. We did not see any bleed caps in the upstairs baseboard heaters so we weren't sure if we needed to bleed in other places too. The system seems to be working correctly and I set it to 55 degrees so the water supply pipes don't freeze. The boiler temperature gauge was 180 degrees F and pressure was at about 20 PSI at that temperature. I assume if the water was colder the pressure would drop. The boiler is about 4 years old. I am totally new to water heat as my last house had forced hot air heat.

1) Does 20 psi at 180 degrees F seem correct?
2) Did we bleed the system properly?
3) At one point I was draining the system and by accident had the water supply off and the pipes started banging (probably because the heater was on and water was draining and there was air in the pipe because I wasn't supplying water). Is there any possibility of damage? I hit the power switch off when I noticed that. I think the banging occurred for about 5-10 seconds in total before I opened the supply and got it under control.

Thanks all!