Andrew
On home rule the problem is your forgetting about the unionist/loyalists/Protestants, call them what you will. It was the problem of getting something that was agreeable to both them and the hard lined nationalist that made Ireland such a problem. If the nationalists had been dominated by people who were concerned to rule themselves then you probably could have had a peaceful solution, and a lot earlier as the hard line unionists would have been isolated. However the extremists on both sides basically made a peaceful solution impossible and isolated and largely destroyed the more moderate elements on both sides.
On the question of earlier votes for Catholics you would have change the history of religious mistrust and hostility in Europe. To get major famine relief you would have to drastically change the standard economic and political theory at the time to get the latter. [Talking about Britain in the latter case here as the standard on the continent was still highly interventionist, although possibly not heavily so in terms of rebellious minorities].
Some form of land reform may have helped, although on its own earlier on it might well have made the famine markedly worse. However again your going to have to change the basic philosophy of the sanctity of property and minimal government in Britain at the time.
Steve