The answer is to put absolutely nothing for the wifi adapter into your
/etc/network/interfaces file, regardless of what other sites or such state to do for configuring a static IP address for an interface. Adding anything to
/etc/network/interfaces for the wifi interface will have Network Manager not manage the wifi device, which is what you saw when it shows no networks.
When working with wireless networks and Network Manager, (or Ethernet connections and Network Manager, it's the same basic process) you have to configure network manager for how to handle the connections. That is, you need to set the static IP in the network settings specifically for a given wifi network, like so for a given network:
That is, I connected to the wifi network (in this case an Xfinity gateway), then afterwards I went into the Network Manager settings via left-clicking the icon and selecting "Edit Connections...", selecting the wifi network, opening it in "edit", and setting the address (in this case, 192.168.215.2), netmask (it's a last-octet-variable network, so all IPs are within the 192.168.215.0 and 192.168.215.255 range, which is 255.255.255.0 for the netmask - or '24' for CIDR range designation), and gateway (192.168.215.1, the router) accordingly for my network. You'll probably want to put
126.96.36.199 into the DNS servers field, though, so you can actually resolve domains.
Hit "Save", close the "Edit Connections" window, disconnect from the wifi network, and reconnect by clicking the wifi network in the networks list. Static IP addressing is now enabled for the network and in effect, so you won't need to rely on DHCP.
You'll need to do this for every wifi network you want to set up with a static IP though. It's not a 'global' setting.