My main PVP build that has the capacity to deal with everything 'meta' based on my testing with randos and RR peeps.
It's got a simple plan, AB > Kick > Charged Linear > Charged melee
Or AB > Charged Melee cancel > Charged Melee > Back Laser > Charged Linear
And any permutation you see fit in between.
The left shoulder can be exchanged with a lot of things tbh, and I've had success with just another laser cannon, the 10 cell missile launchers, and various others. Its bread and butter really are the Laser Lance, the Harris, and the Kick.
In terms of swapping the frame out you definitely can. I chose most of them for aesthetics and usability. I use those legs now over the Verril because it lets me get to 490 Assault Boost Speed with the Buerzel, which can IN THEORY catch up to the Coral Corn Missile Submarine. I have yet to test this extensively.
Extension is Assault Armor because it absolutely counters Pulse Armor at face hugging range if the opponent decides to use it in your face, and it also wards off other melee or CQC users being too aggressive.
It can definitely be exchanged with Pulse Armor for better ACS flush and neutral.
This is also on top of this being a very good mission AC as well, just due to the Harris and Laser Lance just being very good for missions, been S Ranking a few of them since this is also becoming my 'canon' story AC, we are hounds after all, so being a quad feels correct HAHA.