So I've been doing a playthrough of K2 with this mod, and I know you wanted someone to help with K2 balancing, so here's a list of the major changes K2 does:
Armor grid sizes are nerfed - generally by 2x2, so mk2 armor is 8x8 instead of 10x10
New armors - you get a mk3 and mk4 power armor later in the game, with greater resistances and a 10x10 and 12x12 equipment grid, respectively.
Equipment changes - equipment has limitations on what it can work on; vehicles can't use exoskeletons, for instance. Adds new vehicle equipment and higher tiers of normal equipment. Most vehicles have equipment grids.
New weapons are added:
early game, if the realistic projectiles option is enabled, you get a marksman rifle.
late game, you get the impulse rifle (piercing laser), and heavy rocket launcher (only way to fire bigger rockets and nukes).
Realistic Projectiles - If enabled (enabled by default), bullets become actual projectiles with travel time. These bullets can collide with Spidertron's legs, which is annoying and makes it pretty difficult to shoot things.
New ammos - bullet-based weapons get a alternate ammo which hits a little harder and does laser damage.
Radiation - A new damage type, radiation is added. You take radiation damage when near uranium ore or holding radioactive raw materials. By default, holding some uranium is enough to kill you in around 15 seconds, and armor helps with this - with mk2 power armor, you can last over a minute. Not sure if vehicle damage resistances can mitigate this.
Better Tank - A late-game MK2 tank, which is more durable, has a larger equipment grid, gets vehicle mounted versions of railgun turrets (high damage, high piercing, low firerate), a better impulse rifle, and a vehicle mounted version of the heavy rocket turret, which fires a different and stronger type of rocket than the heavy rocket launcher.
As far as balancing goes, I'm not quite sure.
If you're trying to make the Spidertron Engineer on-par with the player if they're wearing the best armor they can make, you should probably:
Add the marksman rifle to the second-tier Spidertron
Reduce the modular-armor wearing Spidertron to 4x4
Reduce the rest by 2x2 (iirc)
Add the impulse rifle and heavy rocket launcher to the mk5
Add a mk7 and mk8 with resistances and grids equivalent to the mk3 and mk4 armor
Adjust the Spidertron Engineer's equipment grids to allow for player-only equipment
And add radiation resistance, though i'm not sure if that will work with vehicles.
If you're trying to make it on par with vehicles, too, then you should probably also add a railgun weapon and a rocket turret weapon.
The main issue I see is that this is a rather lot of weapons - as many as 12, total. There are a few ways to mitigate this; on my playthrough, I modified the mk6 Spidertron and dropped the submachine gun and shotgun (flamethrower could go too, but it's nice for clearing trees in a way that nukes lack... finesse). I also dropped the extra rocket launchers that don't do anything, since the auto weapon switching is disabled.
If you want specific numbers for anything, let me know.
