For your plane 72-100", as you specified.
rudder - most any mini/micro will do. HS-85BB is an example
elevator - same
ailerons - same
flaps - competition pilots land with flaps 90 degrees down for very slow controllable pinpoint landings. if this is your application, metal geared servos are the ticket. Mostly due to gears stripping if you forget to retract the flaps right before landing.
I would favor a fairly strong and well centering servo for the elevator.
If you are planning on building a 120" or larger span, stronger servos like HS-225MG for flaps, elevator would suffice.
Removable wings are common. Basically a steel wing joiner rod, which passes through the fuselage and into the root of each wing is one option. 3-pc wings have two joiners holding the center section and the tips together. Wings are often held together with 3m electrical tape.
Here are a few vendors selling kits similar to planes you describe.
http://www.isthmusmodels.com/pages/sailplanes.html
http://www.skybench.com