My preferred method is shown in the attached photo. First, Build the post assemblies. Drill a plate with a hole pattern (or three pattern locations as shown), and then weld it to the botttom of a 4 inch round tube section. Weld on a cap and finish grind and prime. Put a drain hole in the bottom somewhere. Next, put together (welding is easiest) the structure below ground. You want four 5/8" all-thread segments sticking above the finished concrete, so put these all thread sections thru the post base plate you made, then weld them together (where they will be below the concrete surface) with enough metal to hold them in the concrete, I'd suggest at least a foot deep in the mud. Once you have both parts and they fit well, dig or drill a 12 inch diameter (or larger) hole to below frost level for your area. Pour in the concrete, and set your all-thread assembly. Once cured, set on the post assembly with bottom plate, choosing the hole pattern that gives the gate the correct position, double nut (above and below the post plate) to adjust height, plumb, etc. I beleive commercial hinges are available to clamp around 4 inch tube, but I made my own, so not sure. This system will sag if people climb the gate, but can be adjusted to perfect again anytime you want. I always prefer two shorter gates instead of one big gate. Two 10 footers would make it fantastic, plenty wide enough when both are open, and maybe one can stay latched into a center anchor and only one opens routinely. Just some ideas to consider.
Mine was in place last year and had to be removed to move a mobile home thru. Worked great to unbolt the posts, lay the gate/post on the gournd out of the way, dump some gravel on the footing with all thread sticking out, and the house was moved thru. Put it all back together in minutes. Try that with a post set in concrete.
Oh yea, another benefit is, when someone damages your setup with their car/truck, you can probably tune it up again. Or maybe you have to toss all the above-ground stuff but the concrete and anchors are OK, so you fab up some more above-ground posts to nut on, and new gates from Tractor Supply, and a call to their insurance company to get them to pay...