Am also surprised there have been no further replies to this, though I don't think Oldnick was being too gloomy - I would see it as a healthy dose of realism.
O/p: to have an idea of what rate of tax you would pay on the net rental income we'd need to know rate you pay now - if you are currently at 41% then you will have to pay that on the rental 'profit', plus PRSI and USC.
You say your mortgage repayment is currently €900 per month. If you rent out the property your lender may make you change to an investment rate mortgage (more expensive!). And only 75% of the mortgage interest is allowable as a tax deduction, not the full 'interest & capital' amount. In their election campaign Labour had proposed to reduce the 75% allowable interest to only 25%, so you never know how this will change in future.
You will also need to take out landlords insurance, register with the PRTB, pay the NPPR (2nd home tax, which Labour also proposed to double), pay for any repairs for your tenants, advertising fees, possibly pay for a managing agent, cover the mortgage during periods of vacancy... unfortunately I'm sure there is more!! Oh yeah, you also have to hope that you get good tenants.
You are allowed deductions for the landlords insurance, PRTB registration, repairs/renewals, agents/advertising fees. But in general, I don't envy you.
This is something I looked into for myself and it looks stressful!