Every SSID takes some airtime on some channel. Theres a fixed amount of time and Channels available. If you saturate those, stuff get's dropped. Depending on where you live, there may already be a lot of ssids floating around which have to be considered. Also, because of the antennas used in ubiquitis APs, you can only have 4 or 8 SSIDs per AP.

So the answer is a clear maybe.

As for networks/vlans: more vlans mean more work for the router. But a lot more factors come into play here (traffic between the vlans, number of firewall rules you set up) so its much harder to give you straight numbers. For a standard home user I guess you won't reach a point where the number of vlans impacts your traffic.