Hello Mike I'm a HOG in London hope I'm able to help you & yours out a little here on your quest.
Q6&6b) Yes we have the Europe HOG books here aswell. The contact Address is,
H.O.G. Membership & Rider Services Center, Globe House, 1 Chertsey Road, Twickenham, TW1 1XQ UK
Tel: 00 800 1111 2223, Fax: 00 800 7766 5566,
Email: customerservice@hog-europe.com
Q1 weather) That can be a hard one to call. Weather over here can be pretty unpredictable even the weather man blows it. On that you take your chances, if lucks on your side sun if not rain

Q2 ferry) That would be out of Wales & depends were you wont to be dropped off, by the way, there is a border there (passports)
Q3 renting) HOG should sort that one for you.
Q4 exspore) Well thats a tall order. There is Sooooo much, I my self have not been there, I'd ride the cost line and towns, villages get away from the tourist traps and you get to meat the real Ireland, you can arrange to rent little cotages along your rout.
Q5 time) If you got the time 2 weeks to ride the cost, depending how you posh.
Hope this helps send a PM if you'd like my Tel. in London be glad to lend a hand were I can.

Pete.