These Revenue booklets don't mention any €5K limit. They do mention a qualifying amount lower limit of €315 and an upper limit of €1,270 for tuition fees for IT and foreign language courses though.
I only realised the two year requirement this year when i hoped to claim fees back on a year's course. Also read somewhere that you can't already have done an undergraduate course. Not as straight forward a relief as it first appears and doesn't seem to really encourage further training, broading your knowledge.