I don't have time to watch all of them, but I'd offer some thoughts ...
The side plate and sear pin do not have to be removed at the same time (connected), and there's actually a good reason to remove them separately, which is potentially tweaking the side plate if the sear pin is "sticky" (and it can be at times).
"Snapping" the headed sear pin out to the right (lightly but briskly hitting it with a plastic mallet on left/headed end) requires a practiced technique, though. Then, also being able to install the sideplate over the left end of the sear pin during frame reassembly, without bending the sideplate legs, requires some practice and experience. I use a technique involving using a nylon block to support then right side of the frame (and right end of the sear pin flush with the frame), and then the edge of a maple wedge to snap the sideplate prongs over the head of the sear pin at the same time (to avoid tweaking them, risking bending one leg or even breaking it off).
I stopped watching the frame video at that point and opened the slide link.
The slide video ... I only watched parts of it (jumping here & there due to time).
S&W recommends to its armorers that the sights and extractor are NOT removed for any reason other than repair/replacement. Not for routine cleaning & inspection.
As a matter of fact, during training classes armorers are provided with a pair of classroom guns, one of which is just the "extractor/sight" gun. (In my first class we were given 8 guns, one for the "extractor/sight" training and the others to mix up parts and practice repetitive disassembly/reassembly.)
Why? Because the dovetails for the sights can go out of spec if sights are removed/installed to many times. Ditto the extractor pin hole. The "sight/extractor" slides usually get beaten out of spec at the dovetails & extractor pin holes. I can tell you that removing the sights and extractor pins become VERY easily done in the training guns.
Also, the solid extractor pins are always removed DOWNWARD, and installed UPWARD.
This typically requires the use of a "starter" punch (to get the pin broken free and moving) ... especially when working on older guns ... and then a 1/16" straight pin punch is used to drive out the "freed" pin, downward. The solid pins were installed with heavy presses, and sometimes it took a 2 or 4 oz ballpeen hammer and a brass drift punch to break the rear sights free (slide mounted in padded vise jaws).
Yes, the extractor spring tension can sometimes cause the thin punch to become bent, unless strong pressure is maintained against the extractor (but that also helps create "new" starter punches, using the cleaned up short stub remaining when a 1/16" punch tip is bent and then broken off).
In older 3rd gen guns the solid extractor pins could be in VERY tight, and there was a slight taper to the extractor holes in the slide, with the "top" one (above the extractor) being tighter. This kept the pin from walking upward.
Sometimes it was wise to keep the orientation of the extractor pin in mind when reinstalling one, especially in early 3rd gen (or older) guns, since some were wider at the bottom than the top after original installation at the factory. Of course, sometimes a used pin might require some judicious peening in order to get it to offer enough resistance inside the hole so it didn't "walk". It's easier to simply use a new pin when an old one wasn't tight enough, though.
We were also given some tapered needle reamers to use to clean out any burrs in the slide's holes, and were warned to be careful not to ream out the top holes too much. They no longer give armorers the needle reamers, reportedly because manufacturing methods and tolerances are much improved over those of the older 3rd gen guns. They haven't been offered in the tool kits in last 2 or 3 (3rd gen) pistol armorer recerts I've attended.
We also used to be given offset (dog-leg) revolver files to use to clean up any burrs from the bottom pin hole in the slide. Such burrs could stick out and cut into the alloy frames of the aluminum guns. Newer production slides have a "raised" spot around the extractor pin hole, lifting the bottom of the pin slightly up and a little more away from the top frame rail (unlike the earlier 3rd gen's).
BTW, I've seen what happens when someone unfamiliar with removing extractor pins on a 3rd gen tries to do so by driving the pin upward, and the slide hole was too tight for it to occur. They hammered, gouged and wallowed out the bottom hole (below the extractor). I got it back apart, but the bottom hole in the slide was unrepairable. The top hole was unable to exert sufficient tension, by itself, to hold any new extractor pins in the slide (they'd walk). The slide was toast. Ruined.
Now, I recently learned that S&W has finally decided that they're willing to use roll pins in the place of solid extractor pins. (It's about time.) Probably based upon their last few years of experience using a roll pin for the extractors in their M&P 45 (which was supposedly used in anticipation of a military maintenance spec in the suspected '05 pistol testing).
Then, they apparently slowly decided to switch over to using roll pins in other M&P's for extractors (I just saw one in a VTAC 9mm). That's fine with me, as the solid extractor pins in some M&P's have been VERY tightly pressed in place when I've examined them, and I grew tired of beating on S&W extractor pins many years ago. Made me feel like I ought to be a blacksmith.
It's nice to have the spring plate under the rear sights, but that was a relatively new revision (first saw it in the .45 slides). Lack of a spring plate requires some careful attention when driving a rear sight base off, but
especially when installing a sight base. The springs are too easily damaged (bent, tweaked or even clipped) if the top of the springs are caught against the advancing left edge of the sight base, and the inside of the slide's spring hole, while you're banging away on the sight drift. A damaged spring in either spot can become a potential problem.
When reinstalling the manual safety assembly into the slide,
you may find it helpful to have it lightly oiled ... but it doesn't require lubrication, and it ought to be wiped off before reinstallation in the slide. It's a "dry" assembly, as is the hole in the slide where it fits and operates. Lubricant in that area can migrate not only into the firing pin channel, but into both plunger spring channels, where it can attract fouling, dirt & grit, which may eventually gum things up. (Ditto for not using & introducing excessive solvent/CLP to the manual safety body during normal field-stripping & cleaning.)
Now, it's been a couple of years since my last 3rd gen armorer recert, and I'm sure they've been making further revisions beyond just the extractor pins.
I know extractors are becoming much easier to fit to the tighter tolerances in newer production TSW slides, and the sear release levers are being made within a tighter tolerance range (but I still keep some of the older, over-long levers for any older guns that may require them).
Even though the 3rd gen guns are pretty much only being made for existing LE agency customer orders (if they can't be talked into buying M&P's), they were still making manufacturing changes and revisions, even before they shifted production from Springfield to their Houlton plant. They still have some existing agency customers that are continuing to order 3rd gens.
I'll try to make some time to look at the rest of your video's in the next few weeks.
Of course, I'm neither a licensed gunsmith nor a factory engineer. Just a LE armorer who's worked on the 3rd gen's for some years. I'm NOT an expert.