<"but how do you keep the helicopter still in a hover?">

The easiest method is to turn the transmitter off so the pilot can't move the heli (its a joke, please dont try it, but there is a lot of truth to it)

Since your entering the sideways loop at 40mph with a ton of drag the negative collective is needed to round the top off. Otherwise you end up with an egg shape.

Onto the piroetting loops, this is what worked well for me. Work on stationary piroettes, work on slow flight piroettes (circles, flat eights, etc), work up to faster flight piroettes, then work into fast flight piroettes with chandells on the ends, then work into fast flight piroettes with verticals on the ends (like stall turns), by this point you will probably have figured the piroetting loop out yourself. In other words you earn it............

I spend quite a bit of time in the air, probably 5 hours a week on 3 evenings and all day sunday (planes & helis). To be honest if I had to keep track of it I would consider it a job not a hobby