You either know how to drive standard or you don't! I've driven them extensively both in LHD and RHD and there is no difference - its very natural to make the switch from one to the other.
As long as you can remember to stay on the correct side of the road in Ireland, you'll be fine.
brake in the middle to be used by either foot.
Err, I'm pretty sure that when I learnt to drive (in a manual RHD), I was told that you NEVER touch the brake pedel with your left foot! Left foot is for the clutch only, regardless of what side of the car you're sitting in.