The difference in CityJet between S/O and F/O is only that F/O's have passed their ATPL skills test so basically after 1500 hours (expect about 3 years).
It may not seem like a lot but you will be payed from Day 1 and will have your type rating paid for (although you will be bonded for 3 years). Also all accommodation will be paid for during training - even on your days off. After your line check and release to the line you will get hotel and breakfast on your overnights away from your home base.
Bearing in mind these numbers are a couple of years old for a DUB base so may be slightly out due to the changes in Irish taxes they will not be too far off.
For the first year I was left with about 1500 eur a month after taxes. After a year that rose to about 1900 eur net
pr month. After getting your ATPL you can expect a further 400eur increase. On top of that expect 30 eur
pr sector and 70 eur
pr overnight so an additional 1500-2000 eur
pr month which are tax free in Ireland.
Hope this helps