€650-€700 rent on a 50-60k is high, almost implausibly so. This a regional town with it's own little economic microclimate? If those numbers are correct, the maths might actually work out. You are roughly talking about borrowing at 4% to invest at a hopeful ~9% (after expenses, before tax). In the short term, that could be profitable. Long term, I doubt this imbalance of rent vs value can last.
I'd be uncomfortable with the risk involved. Right now, 75% of your net worth is invested in one address, in one town. In a year's time you're looking to be 90% invested in two properties, in the same town? Sure, if the local rental market corrects itself by prices going up, you'd be quids in. If rents go down instead, you'd be in hot water, likewise if interest rates go up significantly. If the big factory down the road moves to Bangalore, you're cooked.
This sounds like a very Irish situation to be putting yourself into. The numbers suggest you're doing really well - you don't need this risk in your life. Do you want to be a landlord that badly?