If the 1/2 inch is closed on its end then yes. Or if it is at line pressure. The flow rate of what is on its end maters.
Look at the flow rate that you need for each emitter, then use a calculator to see how many you can use on the same line.
Yes you can close unused ones , or use 1/4 inch at that point for a different feed, given that you keep the flow rate in spec.