Correct. The gas block diameter should be .750".
The Oracle uses the low 'A3' Height. I have a Troy MRF 13.8" on mine and it has been working out great. I'm forgot what other brands offer the lower height. Check out Samson and MI.
Any standard AR wrench will work. The Oracle comes with a standard delta ring assembly around the barrel nut. I would suggest getting an LR308/AR10 receiver block and very sturdy vice to remove the barrel nut. They didn't use locktite on the nut, but mine sure seemed like it. I had to put over 130 lbs of torque into getting that SOB off.
I had some small reliability issues when I first got it. It was double feeding a lot but that was fixed when I switched from the stock DPMS mags to Magpul.
My extractor broke at about 600 rounds. DPMS replaced it free of charge. I haven't had an issue with the new one.
It seemed over gassed, so I changed to a JP adjustable gas block. The recoil is much softer now. I would eventually like to get a midlength barrel.
Otherwise, it eats anything that I put in it, even some crappy surplus stuff that my local range wanted to get rid of. It wouldn't fire in any of their rentals.
The accuracy is pretty good. I can shoot a little over 1 MOA using 168gr HPBTs, but that may just be me. It really doesn't like lighter bullets though (maybe because of the 1:10 twist). 147gr ball gave me a 4 MOA spread.