Hi Epeorus,
Welcome to the forum.
We have a few contributors that fish that water, but their visits here are infrequent so there's a good chance this will go off the board before they see it. You'll have a better chance in the future if you stagger your questions over several topics and time frames. Kinda like fishing... If you throw all your flies in the same hole at the same time the results are likely to be poor. :)
I have never fished the water you mention, but I do have a fairly good understanding of entomology as it relates to fishing. Perhaps you'll find my answers helpful.
1. Yep, this is true almost everywhere. Generally, they provide the best fishing very early and very late in the season. Drifting small nymphs then are very effective during periods between hatches and the hatches themselves can be prolific, particularly on overcast days. Again generally, they don't like bright sun.
2. You mention ephemerids, but I believe you're not seeing them because your water is the wrong habitat for them. As for PMD's, I'm surprised you aren't finding them. Like baetids, they are ubiquitous. You should be seeing plenty of them midday or evenings starting about now through most of the Summer. Most of the three tailed flies you'll see should be them or close relatives. The only other common three tailed flies in their size range are the Mahoganies and there's no mistaking those slim baetid-like bodies for ephemerellids.
3. If they have two tails, yes. If three, they are a species of ephemerellid, possibly E. dorothea infrequens or (I'm beginning to suspect) the common but rarely mentioned E. aurivillii
4. Sure. Fly shop reports are often prepared by anglers that are entomologicaly challenged. If the flies that hatch are brown with dun wings, Red Quill is a good catch-all common name - like BWO for green or olive flies with dun wings. In the West, Rhithrogena are generally referred to as March Browns or even Black Quills, depending on time of year, species, or locale.
5. Black Flies are an enigma out West. The only good news about them is that they aren't as nasty as the ones back East. I'm not aware of them being important, either. They can be back East... Having said that, if there are that many in the River it wouldn't hurt to carry a few imitations. You won't find many in stomach samples until you do. :)
6. Maybe, maybe not. Some species will hover over the water and then head back to riparian foliage, others will fall at dark or during the night. If you start seeing sips (especially at the smooth lips of pools), suspect spinners. If the fish are slashing and rolling, stick with your caddis imitations.
7. Green Drakes are often tough for several reasons. Their populations are very cyclic (tending to the downside the last few years in many locations), and their seasonal hatching often takes place when the rivers are still blown. They also tend to like more inclement weather than most anglers like to be out in. During nice weather, they tend to hatch at last light or straggle off during the day. The good thing about them is they tend to get the fish looking up for a decent meal thus providing good fishing with a plethora of large attractors.
8. For reasons that escape me, your observations are mine as well. While what we think of as good facsimiles of the naturals often fail to produce, flies like the Prince (or other attractors with peacock bodies) knock 'em dead. I've long since quit arguing with Mr. Trout about this and just give him what he wants... :)
Hope this helps!
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman