Can I leave an open port when using push-in connectors?
Leaving open ports is fine. They make smaller sizes for space considerations. Combination packs are available, though they are more expensive when not bought in bulk.



Ideal's Twister® wire connectors(p.3) have specifications for the minimum and maximum numbers of wires. Their In-Sure™ push-in connectors(p.15) are only limited by the number of ports and will accept "any combination of #12-18 AWG solid and stranded copper wires".