PCB ground plane separation between power and analog sections of board
You are asking many questions here. Too many to answer thoroughly. So, I'll try to give you some general guidelines &amp; layout hints.

A. In the two designs you present, the analog and digital ground planes are not separated anywhere near enough to be effective. All the common connecting area is  detrimental. You want to have the planes connect at just one place. The position of that "place" on the PCB is important. In general, the connection of the planes should be made thru a wire jumper or zero-Ohm resistor.

B. Typically, the best place to connect the A-Gnd &amp; D-Gnd is where they enter the PCB. In this case that would be near your edge connector. However, wire jumpers being cheap, you should place a number of optional connection jumpers along the dividing gap between the planes. When you get the board completely assembled, you can play with the various jumper positions to see which one is best. (You may find the optimum connection position varies according to the operating mode of your circuitry.)

C. The width of the A-D-Gnd gap matters. The planes will capacitively couple even though they are co-planar. The result is that you end up with a virtual capacitor between the two grounds which provides an inadvertent connection path thru which ground currents can flow. Typically, I make my gaps at least 0.125", but sometimes as much as 0.500 if I have the PCB space to do so and the noise situation warrants. You can test this effect in your prototype PCBs. Before you solder any components to the PCB, connect an LCR Meter between the two ground planes and measure the capacitance. It will likely be in the order of tens or several hundreds of pico-farads. Make a note of this value. When the board is completely assembled and you have tested it enough to become familiar with its inherent noise levels and performance, connect a capacitor of similar value to the measured value between the ground planes. The amount of noise increase you observe in doing so is roughly equal to the amount of noise contributed by the "embedded" inter-plane capacitance created by the proximity of the A &amp; D Gnd planes. This exercise will tell you if you need to make the gap even wider.