from the connemara half to the galway full

Thats a lot of questions.  Okay Running 3 times a week should be fine. You should have plenty of time to train up for Galway.  You are already able to run 10 miles and sound like you will not have much problems completing the half in Connemara. ( I am assuming that you were able to complete the 10 mile running for the whole of it.)
The number of long runs and distance is up to yourself. I would suggest that you have done 4 long runs of 20+ miles before the marathon itself with the last 2 weeks before. Then taper down up to the marathon. If you complete Conn half withou a problem it should be straight forward enough to start extending your sunday run up to this distance and be doing your first 20 miler by mid July say.  With a 5-7 speed session and an 8 mile run during the week that should be plenty for your 3 runs a week.
Those are just my thoughts. If you are just looking to complete the Galway marathon then these are just fairly typical ideas.  However this might not suit you. I would advise you to read up on various training plan that can be found online etc.
Heres a link with a training plan for beginners. Its a 6 month plan but you should be able to amend it to something that suits yourself.  
http://www.sport-fitness-advisor.com/marathon-training-schedule.html
Of course if you can join a running club then you should be able to get all the advice you need there.

BluLou, let me ask a few Q's first.
You did the Craughwell 10, doing the Conn Half, so did you run all the way? What kind of times were you doing/expect to do them in? Main thing about training for a marathon is the long run, so one of your days MUST include this facet, and your pace dictates how long you will likely have to dedicate to this.
The general advice on marathon training is to get out as often as possible in a week and inlcude a long run. I know you said you can only do three, but have a look, do you think you could do an early morning run(s), especially when it hits the height of Summer. Its amazing how much you can cover if you went out 1-2 mornings a week, came in showered, ate and went off about your days business.
But assuming you have 3 days and you want to be able to complete a marathon, then I'd suggest that you have already a lot of base building done if you can run a half marathon. In fact I would use that as the minimum for my long run if you were to start a week after Connemara say. By that I mean, your first long run should be a half marathon, then for the following 2 weeks increase this long run by 1-1.5 miles and on the fourth week, cut back the distance to get a rest, say to ten miles, then start off the following week back at about 15 miles and so on. You should aim to get one or two 20-22 mile runs in.
For the other two days, since you are resting 4 days out of the seven, I'd keep these runs between 8-12 miles. Thats means you are getting some miles into the legs and keeping consistent running pace. I wouldnt bother with tempo, interval etc ect. Maybe try a few races to spur you on but I'm sure it can be done in the time you have available especially since you are already doing 10-13 miles races. If fact it will be no bother

Sorry Rock Climber but you should really be asking that question somewhere else. Whatever about training tips etc I would not presume to advise somebody on an injury.   A good sports physio is who you should be taking advice from.