I haven't given up, my kid and his GF were here for a week, so I packed the scope up. In that time I installed Lubuntu on the RPI3 and even tried it on my laptop but I just didn't like it, so I went with Ubuntu Mate there. I was hoping to get out late, late tonight for some imaging but I'll probably stick with my windows setup for that.
At least I'll have the scope up and ready to tackle this fiasco again
I've tried a few different flavors of linux on my laptop and all can pair and connect and run Ekos/Kstars with very little trouble. Mint, Ubuntu Mate, Lubuntu and even Peppermint all do just fine, just like my windows machine. At least I have that going for me, I can always leave that laptop outside and VNC into it with my windows machine.
Raspberry Pi is a whole different story. I've tried Ubuntu Mate and Lubuntu on 2 different Raspberry Pi 3's, and nothing will allow me to connect. Bluetooth pairing works, binding rfcomm works via command line, and /etc/rc.local, but I get the same error I've documented previously in this thread. Every single time, no matter what steps I take to detect, pair and assign a serial port, all goes well up to the actual point where Indi tries to connect to the Shoestring dongle.
I'm going to try and find another RPI OS that may work, and in the meantime I'm just going to take my linux laptop back to Mint, it was my favorite flavor and I ran it for years. As for the raspberry pi 3 issues, it's beyond me. Doesn't make a lick of sense, and the same issue cropping up on 2 different machines and 2 different operating systems is mind boggling, especially with people claiming they get the exact same hardware to work on their machines.
I ordered a serial to usb cable from Amazon and made my own shoestring-style USB2EQ5 cable. I still have my Lubuntu OS running on the Raspberry Pi. Everything connected just fine. No issues I could see (Other than my lack of knowledge in actually operating Kstars/Ekos).
Telescope control was as expected, I could slew the scope around with Kstars or manually with the scope control window. I could lock back on the Sun (I'm indoors, was just making sure it all worked) and sync and track it.
Some day I'd love to figure out why the bluetooth dongle can't connect on the RPI, that will probably drive me insane. Seriously.
But for now, I'll deal with one additional cable on the mount and consider this a win. Now to learn how to actually use Kstars to do my imaging
Thanks to everyone who helped, if anyone ever comes up with additional info or suggestions on getting the BT2EQ5 working I'd love to hear it. I'm off to Kstars school in the meantime!