How to create a mixed signal pcb
I have not traced every link you've sent, but here are some basic rules that should help you. Mind that some folks will guide you differently, there are some claiming to keep different ground planes and connecting them on a single point. That's possible to implement but much harder IMHO as it is more important to make sure that all fast signals have a ground plane under them without any exception. Separate ground planes only make sense in power electronics where you could create ground bounce issues without the separation. For fast digital systems, decoupling and good ground planes are more important.

In order to understand this, think of impedance at high frequencies in combination with return paths through the path of least 'resistance' (=impedance).

A fast signal has it's return path right underneath the trace on the ground plane. No matter the thick fat copper you might have elsewhere. If that return path is broken by split power planes or any other cause, the signal does not follow the smallest loop to return and instead creates large loops that radiate. Same for the power to fast devices. If you do not decouple these properly by placing ceramic caps very close to the power pins or by not having low inductance via's to ground plane, then you have the same issue with power paths.

Other than that, keeping analog and digital stuff as much as possible separated is good, also running digital and analog traces perpendicular to each other. 
If you have switching power supplies for analog circuits, yes keep them on the digital part then have them filtered (RC, LC or LDO) and pass through to another plane or area.

Mixing analog and digital is not that bad if you understand good design for avoiding EMC issues.