Sounds all normal to me. All 3 of my M&Ps do this.

The first "break" you feel is the trigger bar retracting the striker block then sliding underneath it. The Apex block is nicely rounded and polished. The stock block is more chamfered. Once it reaches the end of the chamfer, it transitions to the flat side. This could also provide a false "reset" as you slowly release the trigger. A full APEX kit will "cure" this. I opened the loop on the trigger bar of my 9C a bit to better time the striker block and sear release. My FS and Shield still exhibit this. I only notice it on extremely slow fire.

If you refuse to use the sear deactivation lever and choose to trigger pull, that's your choice. When you release the slide, the striker engages the sear. With the takedown rotated, there is more room for the slide to move forward. This jams the striker up against the sear and applies more spring tension. The stock striker also has a more severe engagement angle which accounts for some of the pull weight. I can still pull the trigger on mine but it takes more pressure to release the striker. My FS has a magazine safety so I need to put the mag in. The Apex sear geometry is different, which would be my guess why the other does not extend so far and is easier to release.

The dot on the sear is an artifact from manufacturing. There are quite a few existing threads on this. Again, non-issue especially since you plan to replace it.