Rob,
It sounds like you have not yet come to terms with your diagnosis as yet -- why should you? It will take however long it takes. So I wouldn't worry about telling which others until you've decided what you are telling yourself. It will be harder for others to connect with you about what they read or hear from you if you are in the turmoil you are in now. And unless/until you have some kind of event that you want friends to attend, they will feel more guilty if you tell them about contemplating suicide.
Still, though it's early days for a decision as to if/when/how you are going to control your own death day, many of us fully support your right to make those choices.
Indeed, some have chosen the path of very selectively telling friends, for many different reasons, some outlined above. Still, I can't imagine any of our friends who aren't in the know feeling guilty if my husband ultimately chooses suicide (which, actually, they wouldn't know unless I told them anyway and I would imagine such things are often under the rose in Ireland as well). So you've a red herring there but perhaps you wanted to throw it out as part of the acceptance process. It is your life, your death, and friends can be part of it but that is your decision as well. Be as social or as isolated as seems best. It may be a time to hold your most cherished friends more closely, and gradually to narrow your circle to those whom you see truly care.
As an Irishman, you have read:
I balanced all, brought all to mind,
The years to come seemed waste of breath,
A waste of breath the years behind
In balance with this life, this death.
--W.B. Yeats
The one almost universal truth of MND is that you, unlike your friends, know the manner of your death, whether you decide to push it along or not. That knowledge can make you more powerful within yourself as time goes by. Wait for it.