Irish car rental SNN

Never heard of them, but they seem to be legitimate enough from looking at their website.
The seating arrangement in the Opel Zafira appears to be a 2 3 2 arrangement, with the seats in the 3rd row folding down for storage. Good thing, since there's no storage to speak of without folding them down.. Based on one of your earlier posts you said that you'll have a group of 5 - your family of 4 plus a driver - so you should be OK as long as everyone packs light, ie one medium sized bag plus one carry on apiece. Anything more than that and you'll be pretty pinched for storage space. The 3 seats in the 2nd row would be a tight fit for 3 adults but am assuming that you'll have a couple of kids with you so that shouldn't be an issue either.
Since you've apparently opted to hire a driver you can save about 100 Euros by renting a manual versus an automatic.
Sorting out the matter of insurance is always an adventure when renting in Ireland. It's tough to get an apples-to-apples comparison of the various coverages without drilling down into the weeds of the small print, and it might be a bit more complicated for you since the coverage will be for your designated driver - not you. I'd ensure that there are no surprises regarding the insurance before you pull out of the rental car lot.
And to answer your question from another post, many of the rural roads in Ireland are only wide enough to allow a single vehicle to pass. Meeting traffic needs to sort out which one can more easily pull off into one of the designated pullouts provided every couple of hundred yards for the purpose. Not that big a deal (for the locals anyway) but it always takes a while for visitors to become comfortable with the local rules of the road. Should be old hat for your driver.
The street map feature on Google Maps is handy if you'd like to look at some of the rural roads you may plan to travel to see what you (or rather your driver) will be dealing with.

I have rented repeatedly from Irish Car Rentals and they have always been great. They have a US tollfree number that you could call with your concerns. Perhaps you should call them. Many times, recalls are for specific model years, and their current cars might not be at all affected. Many of my European friends drive Opels, and they get great gas mileage. And since you will have a driver, I'm sure they will be comfortable on local roads, no matter how small (IF you will be on any small roads at all).