clutch adjustment

Good question. How much time is too much. . . 5 second increments spaced out over time is probably a good idea. With the plugs out, the starter isn't working against engine compression. Maybe 3-5 bursts, then let the starter cool down, then repeat the series a couple times more.

It isn't clear how long the bike has been sitting up prior to your getting involved with it. If it's anything like car brakes that have been on a sitting car, maybe the steel plates that weren't submerged under engine oil have started oxidizing into the fiber plates, and that is creating your additional binding. You wouldn't find that out unless you pull the cover and disassemble the clutch.

As others have indicated, sometimes revving the engine and dumping the clutch will clean off the plates enough to allow everything to start working properly. But I still think the ATF option isn't going to hurt anything here.

Have you tried overcompensating the adjustment just to see if it will stop binding? Remove all of your free play, and see if the thing gives any more than it does now. I would keep it that way until after you flush everything.

Hope you sort it out.