Staff Council handles OOBs, if I recall. Thus far the only artillery formations I've found are actually mostly infantry, meaning that if you want saturated artillery you're probably better off using independent groups and attaching them to OHQ formations.
I've encountered at least one Monitor GR unit, so can confirm they exist. I think you only really get access to constructing them once you've got access to better engines and lighter armor, though, which would make sense.
And regarding basics: I think Il Palazzo covered it pretty well but a few extra bits: AP is always out of 100, and shown by the rotating arrow symbol under unit stats. See screenshot below, the pink/purple marking. Also make sure you're in one of the move modes (as opposed to just inspecting, etc.) - M for single unit movement, G to move a full stack at once. See red circle indicating I'm in move mode.
(Link at
https://imgur.com/a/BUxoG4R in case I got that in wrong; I've lately had trouble loading images here for some reason.)
I think the manual already mentions this, but be wary of attacking when at less than 100 AP (in other words, both moving and attacking within a single turn). A battle lasts 1 round for every 10 AP, meaning that a given unit needs to call off its attack early if it lacks the AP. Furthermore, most (all?) troop types have a penalty to their attack value for the first 2 rounds of combat to simulate approaching the defenders.
Furthermore, moving decreases readiness which you'll want as high as possible before fighting (it regains naturally every turn).
Thus, the safe/methodical thing to do is approach the enemy in one turn, then attack in the next. Or at least have a decent fraction of your troops attacking fresh. If, e.g., you have a 50 AP unit and a 100 AP unit attacking, the 50 AP unit will pull out after round 5 but the other unit will keep attacking until round 10. So for flanking elements and the like it's less important (and less feasible) to attack with 100 AP.