It's a really neat boat ride up there. I launch at 25 mile state park when I do it just to be half way there. Keep your eyes peeled for sheep and other wildlife.
I've never stayed the night up there but you've got to check out the bakery. It's delicious.
I know you said that you're not camping but the Forest Service does have some killer campgrounds scattered along the way.
Even if you don't end up staying there it's a nice easy day trip up and back. From the launch at 25 mile it only takes about an hour. Some years you do have to be heads up for floating debris... other years not so much.
To be honest I've never fished that far up lake. I fish all winter for kokanee (just about every weekend or so) and rarely go up past 25 mile. By summer they've migrated down lake and I rarely leave the lower basin (from Chelan up to the yacht club) for kokanee. They're still up there... just not as many. Bring your downriggers for sure because they can be scattered from the surface down to over 200'. I usually start with rods from 15' to 50' and move deeper as the day goes on (rarely deeper than about 165' but 180 isn't unheard of).
Cutthroat are scattered throughout the lake and I would expect there to be good numbers. They're usually much shallower than the kokanee.
Lake trout are present throughout the lake but much more numerous in the lower basin where their main prey (shrimp) hang out. They're tight on the bottom in fairly deep water and rarely suspended. Especially once the sun starts to hit the water. chinook are also found in many of the same areas and are caught along side of the lakers. They can have big population swings but are currently doing well.

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Be mindful of the wind. I always be sure to head out early on the way up as the Northern wind in the summer can make for a very rough ride. That’s big water. It’s a tailwind on the way back so not an issue. That’s a beautiful part of the world up there and ditto on the bakery.

 

Last June we did a campout at Mitchell creek USFS boat in campground. Really fun. Launched at 25 mile creek and its was nasty weather. My 20 foot motion marine handled it but it wasn't fun. Storms and wind really make the upper Basin much different than the lower (yatch club down) downtown Chelan and Mason can be calm and you turn that corner and head up through the narrows and it's a whole different beast.

Debris is a concern too. Just depends on the year as others have said.

Just be prepared to turn around. Not much in the way of rescue past 25 mile creek. Gas at 25 mile and stehekin. Hours of operation should be checked though.

Kokanee were in the lower Basin and guys were catching w out riggers in June but they weren't catching the older age class like us rigger guys. Riggers a must for Lakers unless you are going to jig for them.

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We made that run in August this past summer. The 25 mile launch is good advice, but me being the "I gotta do it all to say I did guy" we launched in town. This is in a north river sled mind you. Handed the wife and kids earplugs and turned my hat backwards. Let's get it on! A couple hours later I was trying to convince them we are almost there!
We had a good time hitting all spots mentioned. Kids were asleep in the seats as we cruised back at 30 to 35 mph. Came across a boat that had run out of gas and was adrift. They said someone was on their way with fuel so we pushed on. Really BAD place to run out of fuel. Keep a close eye on the weather because there are not many sheltered areas to take cover.