Chocodove, be sure to listen to John Duffield re: the bug spray. The mosquitos were evil, but fortunately the blackflies were not out yet. I don't recall seeing any yellowjackets.
I think you will have enough water. I took about 3 liters - and that was stupid of me - I should have known I would need more than that. If it had been cool there would have been no problem - but it was warm, somewhat humid, and calm. I only needed my jacket on some exposed parts of the Knife Edge where the wind was blowing.
It took me more than 12 hours - they say to expect 10. You're younger with good knees (I hope), so I'm sure you'll be about average, at least. (I would have made it in 10 if I had gone down the Hunt Trail to traverse the mountain.)
I think the Helon Taylor may be harder than the Huntington Ravine on Washington. It's not as steep, but the constant boulder hopping and uneven footing are difficult. They're both tough trails - I would have to try them both again to decide for sure.
The downclimb from Pamola into the notch is scary - some other (old) guys who were there declined to proceed. Since I'm crazy, I went for it. I can't rate climbs for certain, maybe it's a class 4, maybe not. Then, you have to climb Chimney Peak - same difficulty - and do the whole Knife Edge, starting by traversing the Sawteeth. The initial down and up climb is the hardest part. If you have decent upper body strength you should be fine - there are plenty of hand and footholds.
FYI - as I write this I am in Rapid City, SD - and I plan to do Harney Peak on Weds for my 25th state highpoint. After Katahdin, Harney will be easy. It's family vacation week: I, my wife, and my kids did IA's highpoint on Saturday - that was a real easy one.