You are correct about the steps taken to purge the air from your system .
Close the valve on top of your circulator and attach a hose to the threaded garden hose connection (valve) . Allow the water and air to purge out until you have only full water (no air) . You should not have to fast fill the boiler by means of lifting the handle or sliding the handle over on the water feeder , it should and usually will maintain enough water in the boiler to purge the zones individually.
Perform this sequence on one zone at a time .
Remember to open the valve on top of the circulator when you are finished purging .
The normal operating pressure for most heating systems is 12-15 lbs psi .
This is automatically set by means of the fill valve which has a pressure reducer and regulator built into it from the factory .
Great photos by the way ... it helps us to help you better .
Hope this helps you