a) Probably not, as long as you've got a good teacher who'll show you the ropes.
b) I don't know what the class is like - it sounds like it'd kind of be structured a little like some Crossfit workouts (ie. free weights at a certain reps/speed), which can be good and bad.
Good because generally these workouts (speed + reps) push your endurance and you get a good hit of a workout. (Citation: me, with my crap rotator cuffs and stupid hips, lolz.) Bad because if your form isn't correct, or if your teacher isn't watching/teaching you form correctly, speed + reps can very, very easily tweak joints and ligaments and cause badness.
As for useful - look at the exercises they're doing. If they're doing sort of single-muscle exercises, those probably aren't going to get you stronger overall - they'll be good for making that single muscle get stronger, yes, but chances are the smaller stabiliser muscles won't get worked. If they're doing something like lots of squats, which work the hips, legs, core and back, you'll get more bang for your buck there.
c) Look around the rest of the class and ask someone who looks to be about your level of your fitness what weight they're using - you can always go up/down during the workout if you find it's too much/too little.
no subject
b) I don't know what the class is like - it sounds like it'd kind of be structured a little like some Crossfit workouts (ie. free weights at a certain reps/speed), which can be good and bad.
Good because generally these workouts (speed + reps) push your endurance and you get a good hit of a workout. (Citation: me, with my crap rotator cuffs and stupid hips, lolz.) Bad because if your form isn't correct, or if your teacher isn't watching/teaching you form correctly, speed + reps can very, very easily tweak joints and ligaments and cause badness.
As for useful - look at the exercises they're doing. If they're doing sort of single-muscle exercises, those probably aren't going to get you stronger overall - they'll be good for making that single muscle get stronger, yes, but chances are the smaller stabiliser muscles won't get worked. If they're doing something like lots of squats, which work the hips, legs, core and back, you'll get more bang for your buck there.
c) Look around the rest of the class and ask someone who looks to be about your level of your fitness what weight they're using - you can always go up/down during the workout if you find it's too much/too little.
pssst HAVE FUN!