As what rhbirkelund said, you can think of the Meraki Portal as more of a "management" thing than it is functionality. (At least for APs). If you move all of the APs to a single network, (for example, Access Point network), you can update all of the APs at the same time including firmware, SSIDs, firewall rules etc... That's what we do on our network.
You can find SSIDs and tagging under Wireless -> SSID Availability. You can tag APs by going to Wireless -> Access Points -> Click a square next to AP -> Tag
**BE CAREFUL**. If you have different models of APs, that network may automatically rollback those model of APs to a version that they can work with. This has the possibility of affecting sensors, cameras etc... You'd need to reach out to support and ask them to "Lock" firmware versions.
To add, when you move the APs over to the network, expect downtime if the networks are configured for different firmwares. It may be easiest if you upgrade all the networks your APs are on to a firmware you want to stick with. (Go for firmware version 30.6). Then when you move the APs over, there will be 0 downtime, for they don't need to be upgraded/rolled back to the network configuration.
Nick