Contractors are rostered on a 5 on 5 off system and are used throughout Ryanair's bases i.e. you may do 5 days in Prestwick followed by 5 days in Stansted followed by 5 days in Hahn.
A preferred base can be selected and rostering will try and have you operate from there as often as possible but there are no guarantees.
As far as I know, the salary is paid offshore and therefore tax free, however it is left up to you to look after things like paying income tax, healthcare and pension, etc.
Hope this helps...