a) yes. Most peope speaking German, your language knwolidge will profit while you walk.
b) normal fitness, lots of middle aged people.
Standard:
" easy
** good paths, altitude difference 300 - 500
*** some mountain paths, altitude difference more thän 500 m, perseverance needed
*** steep mountain paths, altitude difference more than 800 m
c) no costs for guide, just buy your own ticket
See their website with hiking programme:
http://www.zuercher-wanderwege.ch/wanderungen.htm