I will eventually have 7 ground wires, and then another 7 neutral wires to connect each. (obviously I'm not connecting ground wire to neutral wires). I plan on installing leviton smart light switches. I found a black colored push-in connector that has 8 ports at home depot. Is it ok to leave 1 port unused? I can buy one for the ground and 1 for the neutral wires I was thinking.
Yes. If you choose to use push-in type wire connectors, you can insert 1 to #of_ports wires into them.
As mentioned in the comments... Some folks don't trust these push-in devices, because of the failings of their back-stab brethren. These devices are listed, and allowed for use by the National Electrical Code. But you have to keep in mind, so were the failed back-stab connectors. So use at your own risk.