It's still just $10 each way, regardless of the number of stops or connections each way. As for your boarding position, is your flight a stop or a connection? A stop will have 1 flight number but a connection will have 2.
If it's a stop, then you stay on the plane during the stop. Once the passengers who are getting off at the stop city are off, the passengers continuing on (through passengers is what they're called) are able to get up and change their seats if they want. Regardless, you will be on the plane before any passengers in the stop city get on the plane.
If it's a connection, then you will deplane and go to the gate for your connecting flight, lining up according to boarding order. In general, as a connecting passenger you are a little bit ahead of people who are beginning their trip on that connecting flight because at the 24hr point you get all your boarding passes for that day at the same time - that puts you ahead of anyone checking in at 24hrs prior to the connecting flight. EBCI just gives you a jump on anyone in the connecting city who also has EBCI.
