I'm not totally qualified to answer the second question, as I admit I am not an expert grappler, and have just two years in submission wrestling.
But basically, the hierarchy of priorities if starting from a standing situation would be: close the distance -> clinch -> takedown -> pass the guard -> control -> submit.
If I am in Guard top, then I want to pass, control, submit. There are various ways of passing the guard for a beginner like me. Over pass, under pass, stand up pass and so on.
If I am guard bottom, them my priorities will be to: sweep, submit, or escape to standing. I can do that in a few ways, I can create space to escape, or break down their posture to control for the sweep or submission.
With that out of the way, I'll dive into your question. If I am guard top, I know my opponent has to do one of two things: break my posture down or create space to free his hips and escape. Basically it then becomes a chess game (to use a tired old cliche). Example, if I have space I can go for an under pass, once I start my under pass I KNOW from understanding these basics that he then needs to make his leg heavy, so if I feel his leg heavy I can not resist it and let is slide down/drop off of me and go for the over pass. If my opponent is equally skilled, he'll know that I am waiting for this and so on.
I've been told before that a blue belt (2 years of training or so) and a black belt (10 years of training or so) will know the same "moves". Much like me and a world chess champion both know how the pieces "move". But the difference in the blue belt and the black belt will be how quickly their brains and bodies react to said moves and feel the pressures.
The priorities of position I can also apply to my Hapkido. If someone has a single wrist grip on me, I know their priorities will be to control me or punch me. So my priority will be to: Guard for the punch (if the hand cocks back in typically bully fashion) -> step to an angle to off balance and better avoid the blow -> and then to either A) escape the grip or B) trap it and move into a lock of some variety. This is just one scenario, but I pick it as it is something that is done from the white belt level and onward in Hapkido, and should be similarly trained across various organizations of the art.
While there are many variables and places for tweaks in both arts priorities, I think you will understand what I am trying to convey. As another Hapkido person, if you grab another Hapkido person's wrist, you both know what the other may potentially do so it will be a game of who can react, feint, etc the other person more effectively since you both know the same "moves".
I hope I didn't ramble and attempted to answer your question.