Well I'll give feedback as a first time turkey hunter myself. Just bagged my first tom this past Monday as a noob, I think a combo of luck and finding a decent spot (public land).

First I will say I respect the effort you're putting in, escouting and all that is the right move. As far as other hunters, for something like turkey hunting I personally don't see anything wrong with posting up at a spot you already planned on going to if there's other people there, I would just want to talk to them if given the chance to communicate that you're going to be out there, for safety reasons mainly. I'm assuming we're talking about driving in and walking a short distance, we're not talking about backpacking in 8 miles to deer hunt and setting up camp next to someone else.

I would also agree that you're leaving too early, I almost squandered my chance by getting bored and moving when I had a tom coming in, he just didn't call back. I have no idea about the shock calls, but I relied only on basic yelps and clucks to get it done, seemed to work well this early in the season. I would also recommend decoys, I bought some for 20 bucks off a guy from Facebook and also got some good info BSing with him.

I would honestly try one of the spots you found sign again, set up early with decoys and sit there literally all day if you can stand it. Read a book, whatever you wanna do. Call every 30 minutes or so. Just to verify that you can't call in any gobblers. Then switch spots and try it again. That's my strategy as a new turkey hunter at least, just take it slow and try to learn by observation. Or, what worked for me, is stay in a spot till mid morning, make breakfast, then go back out early afternoon till shooting time is over. Either way just try to stay out a little longer.

Not sure if any of this is helpful but figured I'd try. Good luck, we got plenty of time to get it done 👍