These are questions that most would have to answer for themselves, because there is no correct answer.
(1). Wouldn't it make sense for me to call the local law enforcement ahead of time to let them know that... I will be open carry[ing]?
I don't call law enforcement to inform them of my wherabouts, my physical description, and what my activites are when I intend to go shopping, go to a movie theater, dine out, or walk to excersize. After advising them of my intent to do something that is lawful and mundane as walking to a convenience store, do you think that they might conclude that I have some sort of motive for telling them about my activities? Do you also think that they, after being told of my plans, would not use the call as justification to contact me to see what, if anything might be used to compel me not to conduct myself in this lawful manner?
You see, the act of openly carrying a holstered sidearm (or the state of being armed in any fashion) is not, and should not be an 'event'. And the less ado we make about it, the less the general public will make of it. You invite the police by telling them what you intend to do and the general public will assume that every time someone openly carries, the police show up. This gives creedence to the arguement that people who open carry waste police resources, while the reality is, police are seldom involved when someone open carries.
This is one of the reasons I discourage mass events that chum the debate with controversy and conflict with anti-gun groups like the Brady Campaign. It gives them a forum that they would not otherwise have, and by engaging them on their level and on what they believe is their turf puts us at a disadvantage.
(2). Wouldn't make sense for me to carry my automatic pistol with the slide in the locked open position, so with a glance you can see it is unloaded?
If you are comfortable with everyone being able to see that your firearm is unloaded and are not bothered by your firearm being exposed to the elements and contaminants, I suppose that it would make sense for you.
You should not, however, expect keeping your firearm in that state of readiness to keep the police from seizing it to inspect loaded condition or search the serial number for stolen/registration.
I feel that there is some benefit to maintaining at least the illusion that the firearm could be loaded, with an empty magazine inserted (where appropriate by law). This doesnt give passers by a full look at a completely inert weapon and raise the question of the utility of an unloaded firearm. It also creates doubt in a criminals mind as to whether it can be employed as a lethal deterrent.