I cannot comment on the date of the introduction of farming to Ireland, but I would resist the notion that farming arose just as a means of feeding temple construction workers. Sure, they would need feeding and on a massive scale, but does that justify the assumption that it is the sole raison d'etre?

It seems more likely that gathering fruits, nuts and roots led to seed sowing and harvesting. Similarly, animal pursuit led to animal husbandry and corralling. The managed herds would need to be moved on to fresh grazing under a nomadic lifestyle. This would evolve into hay and grain food storage and the cultivation of animal as well as human food crops which leads to a more settled lifestyle. Settlement then allows for permanent feature to be built - then you can build your temples.