Over-all, I think it's a workable plan, although I would not have chosen the same bases -- but that's strictly personal opinion, based on my personal preferences.

I would choose Cohb (or even Blarney) over Kinsale, drop one night from Dingle (and add it to Kerry), and I would likely choose someplace like Lisdoonvarna or Ballyvaughan over Doolin, but what you've already 'Booked In' WILL work.

Some of the days will require early-ish starts to complete, but the good news is that there is a goodly amount of day-light in May. 

"Rent car when leaving and drive to Kilkenny for 1 night...seeing Glendalough and possibly Powerscourt on the way."

Since you only have the one night in Kilkenny, were it ME, I would choose ONE, rather than Both.  Each will require a couple of hours to VISIT -- Plus travel time, to-and-fro.  There is SO much worth seeing in Kilkenny:  St Canice's Cathedral and a CLIMBABLE Round Tower, Kilkenny Castle, Smithwick's Brewery -- and SO much more.

Specific answers: "When leaving Kenmare is N71 through the Park to Muckross more practical than trying to negotiate Gap of Dunloe?.... ": 

I Love driving through the Black Valley and Gap of Dunloe -- I've done it about 4 times now -- BUT -- It is NOT a road for the faint-of-heart, and I would NEVER attempt to drive it before the bulk of the Jarvey's have called it a day.  It can be positively jammed full of pony and traps until nearly 5 PM and REALLY slow going.  Even though it IS a Public Road, the jarvey's tend to think otherwise, too.  The N71 from Kenmare to Killarney is Gorgeous in it's own right -- and offers some tremendous views and stop - offs, like Moll's Gap, Torc Falls, Ladies View, Muckross House, Gardens and Traditional Farms, Ross Castle and quite a few others.

Would Westport be too much to include for this one days drive? 

Given your other interests, I would say. "Yes".  I suggest you choose either Roundstone OR Westport, if all you have is the one day. Could you add a stop there (and a drive through Delphi and the Doo Lough Valley?  Absolutely -- but it will make for a long, and rather 'Rushed' day.

Drive to Kenmare for 1 night.....skipping the Ring of Kerry....... Is it practical to take the N71 route through Bantry?

Driving the 'Full' N71 from Kinsale to Kenmare is about 143 Kilometers (89 Miles).  If you drive inland, via Macroom, it's about 97.4 Km (61 Miles).  The third option is partly inland, via Dunmanway and Drimoleague -- and THEN, on the N71, once you reach Bantry -- and that takes 116 Km (72 Miles).    You will do well to AVERAGE about 30-35 MPH along those roads and that is ONLY for Drive Times.  You'll need to add in time for photo, food and 'rubber-necking' stops.  Do you plan to 'branch out' onto any of the peninsulas (Mizen, Sheeps, Head, Bearra)?  Any other 'Must See' sites -- like Drombeg, Castletownshend or Baltimore?  Those are actually South of the N71, on smaller, Rural Roads that will add both miles AND drive time.

As my 'tag line' says -- What are YOUR interests?  What do you want to see, do and experience while in Ireland?  Knowing that will help guide our answers. 

If the weather is good and you get an early start, consider following the R600 out of Kinsale, through Timoleague (Abbey) and join the N71 in Clonakilty.  The drive from Bandon is also picturesque, but you'll see more of the coast following the R600.

If you plan to deviate from the N71 to visit Drombeg (Which is a terrifically photogenic sight, by the way!) you will probably take the R597 out of Ross Carbery (gorgeous waterfront / swans and ducks!) and then follow signs onto an even smaller, local road.  Departing Drombeg, return to the R597 and it will return you to the N71 at Leap.

Before that, though, you'll pass through the delightful, bayside village of Glandore, which sits directly East of Union Hall.  The single-lane bridge connecting the two is quite interesting.  It (and the two villages) played central roles in an old film called, "War of The Buttons".  I think you might find it worth a few minutes to cross it and snap some photos.  You will pass within feet of it, as you exit Glandore.

Thanks!  Someday, I hope to know 1/2 as much as Michele does!   

Although the R115 isn't the quickest -- or shortest -- route, it IS the most direct, assuming your pick up point is the Hertz Office on South Circular Road, Merchants Quay,  It's pretty scenic, as well, but rather desolate for stretches.  The drive's only about 47 Kilometers (30 miles), but you'll need to allow 1 - 1.5 hours for the drive.

Departing Glendalough, I would take the R756 to the N81 and then continue onward to the M9, at Castledermot  (which is worth a brief stop)   http://irishwalledtownsnetwork.ie/page/castledermot/castledermot-info

There are numerous other potential detours, as well, but I'm trying to maximize your Kilkenny time!   

Map:  ( Figure an average DRIVE time by dividing distance by 50 - 55 KPH -- That's roughly 30 MPH.  You'll do better than that on Motorways and most 'N' roads, but 'R' and 'L' roads will often be less. ) 

https://www.google.com/maps/dir/Glendalough/Kilkenny/@52.8625796,-7.0513121,10z/am=t/data=!4m14!4m13!1m5!1m1!1s0x486797d94279f67b:0x1800c7a937df36a0!2m2!1d-6.32984!2d53.01198!1m5!1m1!1s0x485d30a13423c5ab:0xa00c7a9973173c0!2m2!1d-7.2447879!2d52.6541454!3e0

Thanks for the feedback. Nice to hear from someone that has stayed in some of the same places. Enjoy your trip back.

Tim

Although we can't physically come with you, we can in spirit by offering our advice in advance. That's why you are here!

Since you are driving the Dingle Peninsula you could go one way onto it and another way off. That way you are not going over the same route twice. There are beautiful beaches everywhere on the peninsula. Look for signs that say Tra (means beach in Irish). Inch is spectacular. I have walked the whole 4 miles of it but you can also drive it (carefully as the rental company insurance doesn't cover accidents off-road). I would go through Tralee and Castlegregory (wonderful beach in Castlegregory) then Connor Pass. Come off the peninsula via Inch. That way all bases are covered.