Dear Jonathan,

     Not sure everything gets installed by default. One of the bad 
things of Debian and others was that a lot of applications were 
installed by default, applications you don't even know they are there, 
and what they are for. These apps not only take space on your disk, but 
slow down or even complicate system updates by their sole presence. 
Suppose you haven't a wifi interface; why would you need a gui to 
configure it?

     I will only answer your first point, since I have nothing to add to 
what Steve Litt replied to the others.

     For the first question, I currently use three apps, wpa_supplicant, 
wpa_roam and wpa_gui, currently in two packages in Wheezy.

     wpa_supplicant talks to your wifi interface, taking instructions 
from its configuration file. It selects, from the list of wifi stations 
you have put in the config file, which one it can connect to. wpa_roam 
is a helper application which allows the system to invoke wpa_supplicant 
when your wifi interface detects a network. Description in the following 
howto: http://www.debuntu.org/how-to-wifi-roaming-with-wpa-supplicant/

     wpa_gui is a helper GUI to fill the configuation file. You only 
need it when you must connect to a new station or something is going 
wrong. It can scan the network, so that you can select a station, then 
help you writing the properties of the station into the config file. You 
can also use it to connect/disconnect.

     I discovered the name of wicd on this list recently. I didn't try 
it, therefore I can't compare, but it looks that it has more diverse 
interfaces than wpasupplicant, CLI, GUI and even Curses. I will probably 
try it the first time I install Devuan on a laptop.

     I imagine neither wpasupplicant nor wicd will be infected by 
Systemd, and you'll have the choice between them.

     Didier