for the zoo hub it is a splined sprocket you need, and visit sheldon browns website for advice on wheel building thats how i learned
heres a link My link
the creaking is normally just dry parts flexing and rubbing against eachother.
to get the cranks of you can always hit them with a hammer but just be extrememly carefull not to damage them.
if you cant get them off just spray some lube in round the splines and it should be ok
take cranks of and take the bb out and grease all threads and the isis splines, also grease your pedal threads and give them a check over this should sort it all out, give everything a good clean before the regrease
this is basically what you will need if you are just planning on going singlespeed and keeping your rear hub My link
what size front chain ring do you have that will depend on what rear cog you will need
do you mean the headset, if so its best to get a bike shop to remove and refit the headset. It can be done with a hammer and screwdriver but the chances of something going wrong are higher
and by not powerfull what do you mean, is it lacking bite/hold or both
when your pads hit the rim can you still pull the lever further to your bars?
final question are your pads set up perfectly square to your rim