Sorry, one movement only provokes one AoO from a given defender.
See the d20pfsrd:
If you have the Combat Reflexes feat, you can add your Dexterity modifier to the number of attacks of opportunity you can make in a round. This feat does not let you make more than one attack for a given opportunity, but if the same opponent provokes two attacks of opportunity from you, you could make two separate attacks of opportunity (since each one represents a different opportunity). Moving out of more than one square threatened by the same opponent in the same round doesn't count as more than one opportunity for that opponent. All these attacks are at your full normal attack bonus.
So if you shriek "SERPENTINE!!!" and run circles around your opponent, they still only get one "leaving a threatened square" AoO on you.
The opportunity from Hold the Line is different, but only works once upon them entering your threatened area. So you would get only one from Hold the Line and one for them leaving a threatened square.
Note that the leaving a threatened square is per round - not even just per turn - with the Mythic rules in use in our WotR campaign we've been finding a lot of cases where you get to act multiple times in a round, even charge multiple times, etc. If by hook or crook someone charged you, ran off, charged you again, and ran off again over the course of a round (on their turn or across multiple turns), you would still only get 1 AoO for them leaving your threat but could get multiple from Hold the Line, if they actually leave and enter your threatened area with a charge twice. Up to the limit of the number of AoOs you have.
A creature that, because of the creature's size, provokes attacks of opportunity for entering a foe's square provokes attacks of opportunity when entering that foe's square even if the creature enters that square by taking a 5-ft. step...
The rules cited in the question are from two different places about two different things. The 5-ft. step rules don't care about the creature size rules, and the creature size rules don't care about the 5-ft. step rules. The two rules are managed independently and don't interact. Thus, when a Tiny, Diminutive, or Fine creature enters an opponent's square, it provokes an attack of opportunity even if it entered that opponent's square by taking a 5-ft. step. That's a function of the creature's size exclusive of the creature's 5-ft. step.
Example 1
A Tiny, Diminutive, or Fine creature takes a 5-ft. step when adjacent to opponent and within that opponent's threatened area that doesn't provoke an attack of opportunity (because of the 5 ft. step) and moves into his opponent's square which does provoke attacks of opportunity (because of the creature's size).
When a Tiny, Diminutive, or Fine creature takes a move action to move within its opponent's threatened area then enter its opponent's space, the creature probably should provoke attacks of opportunity twice, once for the movement within the creature's threatened area and once for entering the creature's square, except that the FAQ (see below) says to treat the opportunity granted by moving within a creature's threatened area as part of the same movement needed to enter a creature's space. Thus a typical Medium creature gains only one attack of opportunity against a Tiny foe that takes a move action to enter the creature's square.
Example 2
A Tiny, Diminutive, or Fine creature takes a move action to travel 30 ft. to enter an opponent's square. The creature provokes an attack of opportunity when moving within the opponent's threatened area as normal then can enter the opponent's square with impunity.
It's sort unfortunate that two attacks of opportunity aren't provoked. It might've saved the Dexterity 13 commoner with the feat Combat Reflexes from death by house cat.
...And the FAQ agrees
The Pathfinder Roleplaying Game Core Rulebook FAQ contains the following exchange:
Question: In the section on Tiny and smaller creatures, it says that entering a creature’s space provokes an attack of opportunity, but typically 5-foot steps don’t provoke an attack of opportunity. If a Tiny or smaller creature took a 5-foot step into a creature’s space, would it provoke an attack of opportunity?
Answer: Yes. Even with a 5-foot step, a Tiny or smaller creature entering a creature’s space provokes an attack of opportunity (unless it is using a more specific ability to avoid the attack of opportunity such as the Monkey Shine feat). This doesn’t mean that a Tiny or smaller creature entering a creature’s space and moving out of a threatened square with a move action provokes two attacks of opportunity from that creature, for the same reason that moving out of multiple of a creature’s threatened squares in the same move action doesn’t provoke two attacks of opportunity.
This exchange was added to the FAQ in Jan. 2016.
Best Answer
Correct.
Pathfinder is generally played on a grid representing 5-ft. squares, so two squares would be equivalent to 10 feet, yes. Distances aren’t really measured in squares, though, unlike some other systems (e.g. D&D 4e).
No, or at least not unless you have something additional beyond what you have mentioned here. Attacks of opportunity are provoked only for leaving a threatened space, not for entering it.
Correct.
Actually, it’s up to your Dex mod plus 1. The feat specifies a number of additional attacks of opportunity up to your Dex mod, so that’s in addition to the one you always have.
Aside from that, correct. Note that Combat Reflexes also does other things.
As already addressed, false.
Even ignoring the bit about entering squares, and assuming a similar scenario but one in which the target exited multiple squares, false. You would only ever get one attack of opportunity for something like this.
Generally speaking, you only take one attack of opportunity for a given provocation. Moving out of a threatened area is a provocation, and they do provoke each time they leave such a square, but it’s all one provocation. You can only take the attack of opportunity for it once. You can choose not to take the attack of opportunity and then take it on a later square, if you like (though you risk the enemy not doing what you thought he would, and not provoke again). But the point is, you only ever get one attack of opportunity for it. Combat Reflexes just means that you could also take an attack of opportunity if someone else moved, or if the same person did something else that provoked, e.g. cast a spell, or used a ranged attack, or whatever.
This can get kind of complicated, for example, if someone casts a spell that makes a ranged (touch) attack, they provoke two attacks of opportunity from you, and you can actually take both. One provocation is casting a spell in your threatened area, the other is making a ranged attack in your threatened area.
But for movement, they only provoke again if they make some kind of separate movement. That usually (always? can’t think of any counter-examples off the top of my head) means a separate action.
Oh, and also, it doesn’t matter at all that the hostile moved from 10 feet away from you to 5 feet away from you. Leaving a threatened space is the only thing that matters. An enemy circling around you at a distance of 10 feet would also provoke twice (but again, you could only take the attack once).