It's a great time to be up there. The crowd is gone and you really have a lot almost to yourself.
This is coho or silver time for the Kasilof River. The last time I fished there in August was about three years ago if I remember right so the limit on them may have changed. It was a three fish per day limit then and no yearly number. It is a blast using eggs with only an ounce or so of weight. These are big silvers and in shallow water its lots of runs and air time.
You might want to book a guide once to show you how if you have not done this before. I think there is a run of Humpies in the Kenai River about this same time, however I seem to remember that they are an every other year fishery. If you e-mail Bob the really big one I'll bet he could tell you for sure. We used purple and white spoons on them. Good grief those are ugly lures or I wouldn't have remembered. As for the butt fishing, please don't take my comments the wrong way. Homer is a super fun place to fish out of but........
The run time out of Homer for halibut is getting longer and longer. Not a problem if you like to take long boat rides for butts. Deep Creek boats will give you a shorter ride to the fish.If you are not opposed to increasing the knowledge curve, or your plans aren't firm, I would recommend doing one of each. If the water is rough on Cook don't do the Deep Creek trip as they will not be able to get you out onto the better grounds. I think there is a little more rain in August but its not cold.
Hope this helps a little. Post how it goes. Oh, make sure you buy a derby ticket for silvers in Soldotna. I'm guessing they still have that derby. You may come home with a lot more money than when you left.