If you've got a 22 chainring on the front you'll need a 16 tooth sproket on the back to achieve a gearing ratio of about 1,4
It's a pleasure to help anyway! ^^
There is now problem with the original hub, it's a freehub so the freewheel (not a very good one alas..) is built into it..you just get rid of the original cassette and then throw the spacers and the sproket on and close it using a lockring tool.
If you want some more photos of my setup just tell me, if you want to see something particular to understand how it needs to be fit I-ll be happy to post them this evening