Bicycle Tutor

I'm switching my daughter over to a Profile Elite freewheel. She is currently running a 20" fixed gear with chainring size 44T and rear cog Profile 16T. I understand that I will need a new rear hub and driver...
1. What else will I need?
2. How does changing over to a freewheel change the gear ratio? In other words, how do we know what size chain ring to use with the freewheel?

Good morning, being the fact I am working on my first cup of coffee it's pretty simple. The more teeth in the front (chain ring) drastically changes the "gear ratio" to a harder pedalling. The less teeth in the rear will change the gear ratio to a harder pedaling aspect too. Other then those figures the "freehwheel" will allow your daughter to pedal backwards without having the braking effect. So you will need front and rear hand brakes in place of the old "coaster brake". The gear ratio you currently have is pretty normal for 20" bikes. If she wants it to go faster make the rear cog 14t or 12t. Won't be much but a considerable difference.