You might want to move initiative to Wis to help keep ability scores balanced since your Str/Dex chagne makes Dex stronger while your Wis/Cha makes Wis weaker. But that probably isn't a huge deal either way.
"Realism" based changes on muggles do them no favors, and removing even more things from strengths purview only serves to make it a more superfluous stat.
Brutish who hits hard but not often is anyone who chooses to use Power Attack.
Realism is not a goal of a game of any description, but fantasy less so, and is a houserule that royally screws over muggles more than they already are, even in E6. The goal of the game is genre convention and gameplay.
Dex already governs many, many things already, and it's easy to get damage from sources other than strength.
This is a poor plan built on poor logic.
Paired with splitting melee? Taking away power attack and the other damage boosters and shifting to armor as DR all comes together to make your general approach "take things away from muggles."
Nonmagical characters in Pathfinder need help. Not their few meaningful options taken away.
You're talking about gutting muggle damage options in order to force them to take a stat that only really affects damage, and only a little bit.
As to the armor as DR? A lot of the variant rules are half-baked ideas that don't actually work particularly well. This one's a huge pile of unintended consequences that is useless against a lot of foes, turning you into a sitting duck, while turning others into trivia. There's a reason in the stock rules treat DR the way they do. Bypasses at low levels. Kept out of player hands more or less save for a point or two until higher levels where it doesn't matter. It's 'cuz the way Pathfinder's structured, DR doesn't work very well as a primary defensive mechanic.
There are games structured around armor as some form of damage soak. They scale hit points and damage very differently. Meaningful attacks that can deal one point of damage before soak don't exist. Shadowrun, as an example, uses soak pools. The basic heavy pistol that's the smallest weapon you're liable to consider a serious weapon starts at 8 damage. An assault cannon? 16. Health pools start at a value and doesn't stray too far.
In Pathfinder, you need DR at a value that lets the Rogue precisely swinging a dagger that deals 1-4 damage to coexist in a sphere with a hill giant that deals 12-26 damage. The correct DR value for that does not exist.
To get DR to work in context, you would need HP, damage, and DR to all scale in a relatively narrow band with regards to level. Pathfinder, as structured, is all over the g~!~~~n place.
Also, unless you are a caster, damage does not scale with level as a PC. It scales with all manner of odd and sundry abilities that you just made a note to remove from the game. Nor does AC, which you're also skewering. Meanwhile, AB and HP do, which is one of the roots of a lot of the problems you run into fiddling with the game's core mechanics.
Anyways, if you're making AB keyed off of strength, at a bare minimum, you'd need to combine strength with constitution into a unified brawn stat that may actually be worth caring about instead of bypassing outright. Hell, while you're at it, instead of moving will saves to charisma and turning wisdom into the useless mental stat, may as well eliminate it outright. Maybe rename "Wisdom" to "Insight" and have it take over some functions. Move diplomacy to insight, bluff to intelligence, and intimidation to brawn so everyone can do some social stuff and every stat matters to pretty much everyone.
But more reasonably? You're getting well out of the realm of houserules and into the realm of game design, and that's just a huge headache. Better to either play closer to the book, or just run a different game. Sounds like you want to tone down the fantasy, but you're starting with one of the highest-magic properties on the market, and Paizo's approach is to crank everything up to eleven. Next step up the high fantasy tree is Exalted.
Maybe you'd be better served trying something that's made for a lower-magic baseline. Blue Rose/Dragon Age, Savage Worlds Fantasy, Burning Wheel. Even 13th Age. All way easier to keep toned down than Pathfinder.
Encumbrance is not really a rule worth tracking. It's a convenience, more than a perk. There are enough ways to futz with it that it really shouldn't be considered much of an asset. It's accounting, more than benefit, given the myriad ways there are to mitigate.
Now, as to DR specifically in E6? I stand by my statement.
Let's look at level 1. You put the fighter in chainmail. DR5. You go up against goblins who maybe deal 1d6 damage, and therefore, setting aside crits, deal 1 damage one time out of 6 hits. You're basically immune to goblins. And the hill giant above was not an accidental choice for the high-end monster.
Meanwhile, AC becomes an effectively meaningless mechanic. There are a lot of classes who just give up on the AC race already. The difference between an enemy having an 85% chance or a 95% chance to hit you isn't particularly meaningful, so oftentimes, it's more beneficial for a lot of classes to just drop off the bottom of the AC race and allocate these resources elsewhere. If armor stops being a source of AC, that becomes a more likely decision for almost everyone.
The reason Pathfinder in general and D&D in particular have used the armor as AC model is, given the broad range of damage values, it progresses more smoothly, so long as AC generally scales at a similar rate to AB and stays in a relevant range. DR... doesn't, in the context of this game.
If your goal is to simplify things, then more complications to fix the complications you introduced with your houserules is not sound design. Called shot rules are seldom graceful, and there's a reason they're not included by default.
Then, there's the matter of bypass. Mundane armor is bypassed by magic weapons. Magic armor is bypassed by adamantine. Adamantine armor is /-. Adamantine weapons are quite accessible, at only +3000g, while adamantine armor starts at +5000g for light armor.
Now, let's go back to that hill giant. It's subject to these rules, too, and loses its natural armor bonus to AC, instead getting DR. Its AC therefore goes from a relevant-but-surmountable 21 to a paltry 8, and it instead gains DR 13/adamantine. Or rather a stacking DR 4/magic from armor and 9/adamantine from natural armor. And there is no reason for the PCs to not be swinging around adamantine weapons at this point, ignoring those 13 points of natural armor, and with attack rolls such that AC drops off the bottom of the randomizer, so the hill giant trades 13 points of armor class for... nothing.
Meanwhile, adding in a new called shot maneuver is another layer of complication, going counter to the simplification goal.
In high damage variance games, which Pathfinder is, it's much simpler and more practical to model armor as a thing that deflects damage, rather than a thing that reduces it. Also, it's an extra math step. Extra math steps are almost always an increase in complication.
As to choosing your stat to hit? Feat Tax rules of various stripes are pretty standard. The weapon finesse feat, as a notion, is a horrible design decision, because it's not a feat that makes you better. It's a feat that lets you exist in the first place. A tax you have to pay just to be, say, a melee Rogue at all. It's an ability that you should just have as an option. And there's a reason later games do away with it. Starfinder, 4e, 5e.
On the topic of simplifying things in general? The binder of houserules, which this seems to be fast becoming, always makes things more complicated. I mean, you just linked a seven-page pdf on what you're doing to replace, "Roll 1d20+CMB. If it's more than the CMD number on so-and-so's sheet, you do the thing."
Changing things adds a layer of complication, in that it's more documents that you have to reference and cross-reference. What's more, replacing systems causes much more complication and unintended consequence than tweaking them. See the above linked feat tax rules' approach of lumping together the basic combat maneuver feats into "the one that lets you do skillful stuff" and "the one that lets you do brutish stuff."