Questions regarding Shield Block, Refocus, Splat Book Power Disparity, et cetera

Some questions regarding Pathfinder 2e.

1. Free Archetype
Are there specific Archetypes I should be restricting due to issues of balance, or are they all reasonably balanced? Any that I should keep my eye out for to ensure they don't break my game?

2. Classes, Ancestries, et cetera Beyond the Core Rulebook
I just started with the core rulebook only, since I am a neophyte to the system, but there is an understandable eagerness of the player base to delve into the newer, shinier toys. This is something I am a tad reticent as power creep in splat books is a real concern, though I would love to give them room to soar.

How do later books, such as the APG and beyond, compare power-wise to the what's in the core rulebook - any glaring concerns?

3. Shield Block
With Shield Block (pg. 266) the line "You and the shield each take any remaining damage, possibly breaking or destroying the shield", if 10 damage is leftover after the Hardness does it split 5 and 5 for you and your shield, or do you read it as you and your shield both take 10 damage?

4. Refocus
The requirements for Refocus (pg. 300) are a bit confusing to me as they state, "...and you have spent at least 1 Focus Point since you last regained any Focus Points".

My druid has 2 Focus Points, which can used to cast Tempest Surge, by my reading it seems he would have to Refocus between each casting as he could not Refocus the second time he has not spent any Focus Points since his last Refocus and can only get 1 Focus Point of the two back. If that's right, it appears the upside is that he can drop a Focus Spells twice in a single combat, but only once in a day.

Appreciate any help that can be tossed my way.

1. Whether or not the archetypes are free, I'd say the main thing to look at is that some of the archetypes published in adventures instead of rulebooks get a bit janky or actually specific to the adventure promise and should get a closer look before allowing them.

2. If anything, the classes and ancestries from the CRB are probably stronger, and many of them have a very high "floor" on their performance level (alchemist does have a low floor, because they operate far below their potential without a good spread of alchemical items being used, and figuring out how best to split up reagents between the alchemist themself and things to be used by other party members, though their ceiling is fine, but basically every other class in that book performs very well even for beginners).

3. Both the character and the shield take 10 damage.

4. This is correct, refocusing more than one point without mid to high level feats isn't an option for most classes. Oracle and Psychic have their own things going on, a bit. This is one of the things that is going to change in the remaster, though.

1. Whether or not the archetypes are free, I'd say the main thing to look at is that some of the archetypes published in adventures instead of rulebooks get a bit janky or actually specific to the adventure promise and should get a closer look before allowing them.

2. If anything, the classes and ancestries from the CRB are probably stronger, and many of them have a very high "floor" on their performance level (alchemist does have a low floor, because they operate far below their potential without a good spread of alchemical items being used, and figuring out how best to split up reagents between the alchemist themself and things to be used by other party members, though their ceiling is fine, but basically every other class in that book performs very well even for beginners).

3. Both the character and the shield take 10 damage.

4. This is correct, refocusing more than one point without mid to high level feats isn't an option for most classes. Oracle and Psychic have their own things going on, a bit. This is one of the things that is going to change in the remaster, though.

Appreciate the replies HammerJack!

1. Free Archetype

Are there specific Archetypes I should be restricting due to issues of balance, or are they all reasonably balanced? Any that I should keep my eye out for to ensure they don't break my game?

I don't think there's much of a balance concern with Free Archetypes. For the most part, they allow characters to do more things, but not be much better at the things they already do.

There are a couple of exceptions, with the fighting style type archetypes, where maybe martial characters end up getting all of the class feats they would want instead of having to pick and choose. Even that doesn't seem like a huge deal, though.

My personal preference is to dictate a couple of choices for a character's first archetype, then let them choose freely once they've taken the required dedication plus two additional feats. Typically, any restriction would either be based on some sort of shared background for the campaign, something I thought was particularly appropriate for the background they came up with, or maybe just anything from the "Profession" tab on the Archives of Nethys.

I don't think you'll break anything if you just give them free rein, though.

There are some archetypes that are stronger than others, but none of the archetypes are going to "break" the game. In general no single character is going to break the game via the character build. Two characters working together to build off of each other's abilities can become very effective, but that should be rewarded.

If you're worried about free archetype, my preferred way to implement free archetype rule is to actually choose a set of archetypes that are thematically appropriate for the kind of campaign you're running. Like if you're running a pirate campaign, then the pirate archetype makes sense. But you might also let something like a storm order druid be a free archetype too. And there are probably others that would be appropriate too.

Regarding concerns about later books have power creep...generally speaking later book releases of classes and archetypes does not have power creep. In fact three of the most powerful classes are found in the core rule book. Fighter is probably the strongest martial character because the +2 to hit is that good. And rogue is the strongest skill based character, with a not bad chassis for opportunities to deal damage but it lacks defensive capabilities for staying in combat taking a lot of hits. Bards are the best buffer class by default, while also having full spell casting abilities, and the powerhouse of the Occult spell list.

Regarding shield block, yes both shield and wielder take 10 damage.

Your understanding of focus is also correct.