I've got a bit of time between tests here so let me throw down some example numbers and shit to help you (and me) get a better handle on the system.
So lets start most basic, right? It's what you'd start with in game before you researched anything. The basic frame would be quite lacking in terms of slots and have iffy stats. For instance it might have the following slots
1 head
1 chest
2 per arm
1 pelvis
1 per leg.
Now, armor does not take a slot, it's built in over slots so you can always throw on armor. The main restraint on being a great big mech armadillo is the fact that armor costs money and has weight. Slower means getting hit more, so you need to balance your ability to dodge with your ability to take a hit if you mess up. In case you're wondering the way I'm considering running weight and its effect on speed is like this:
Your weight maximum and your speed are basically the same number, but multiplied by 100. So if the frame's base speed is 12, it means that the weight capacity is 1200. And when you add weight to that, you subtract from that number and that eventually subtracts from the speed of the frame. For instance, if the weight capacity is 1200 and I slap on 500 weight, the amount left is 700 and my unit's speed drops to 7. Simple, right? And parts that increase your max load will increase your speed by making it easier to carry more. Oh and in case you're wondering, the frame itself has weight, but it only comes into play if a limb or something is lost. For instance, an arm might weight 300 units, so when a mech loses its arm in combat, it gains a +3 speed bonus because it is lighter.
So our basic frame would have 9 total slots and each part would have its base HP. For this starter frame lets call it 50 HP per limb or head section and then 100 HP in the chest. Now, I want to start putting stuff into this thing to get it running. The basic cockpit can only go in the head, and the basic reactor only goes in the core, so those slots are filled just to get the thing running. The reactor is pretty heavy and robust (100 HP) but the cockpit is light (20 HP) so we're still running pretty fast. In terms of weapons there are a few choices. Energy weapons use a lot of power but they usually have no ammo restrictions and are good against certain armors. Powered kinetic weapons such as rail guns or pile drivers deal more damage than standard kinetic weapons but usually require both power and ammo. And Kinetic weapons like cannons and missiles need minimal power (Ie in terms of drawing energy from the reactor they need zero, but if wiring is damaged they can still be rendered unusable), but are usually weaker and have strict ammo restrictions. Of course, this isn't universally true for anything, just a general idea.
I want to stick a tesla arc (50 HP) into the fist of my mech, because the only thing better than a big ass punch is a big ass punch that also has lightning on it. Tesla arcs are energy weapons, and drain a big chunk of power each time they're used, regardless of if you hit or not. For sake of example, lets say that my reactor can put out 300 power each turn, and can store 1000 in reserve. The frame has its own requirements, though they're fairly minimal . Lets say combined, all the parts of the frame eat 50 power total a turn to remain active. So we have an effective 250 power per turn. This assumes you're running the frame parts on optimal settings, you could run minimal and have decreased stats or max and boost your stats. We'll assume optimal for now. My tesla arc has a minimum power of 300 to use once, but has an internal battery that can store up to 900 energy. As such, I'm probably gonna set the power systems such that at least 50 or so power is automatically routed to those batteries each turn, just so I'll have some power built up for using it.
In the pelvis I'm gonna put a big ass missile. Because innuendo. And though that missile takes no power, it is pretty heavy, so it slows my mech down a fair bit. In order to compensate, I'm gonna stick a hydraulics booster in the right leg, increasing my carry weight and thus negating some of the speed loss. I'm also gonna stick a targeting system in my cockpit. It takes energy to use it, but it gives a bonus to hit with the missile and makes targeted attacks easier.
Next I'll give my mech a ranged weapon. In this case I'm gonna go with an external weapon, one the mech will hold in its hand rather than one built into the arm. External weapons are good in that they don't take up slots, but bad in that they tend to be somewhat limited. Melee external weapons are all basic kinetics (at least at start) that can be knocked from your hand or destroyed, and ranged weapons have less ammo than integrated counterparts. But they can be ditched without specialized cockpit systems. In this case I'm gonna give my mech a scatter gun, A tri-barrel giant shotgun that fires a cloud of shrapnel. It hits lots of parts, but does low overall damage.
At this point I'm happy with the loadout so I'm gonna armor up a bit. I'll stick another hydraulic booster in the leg, to get some more carry capacity, and then put two layers of armor (50 each) on the head and 1 layer on the chest. Then 1 layer on both slots on the melee arm, just to prevent it from being severed so easily. The head has 170 HP at this point, the chest 250, and the melee arm has 100 on the top slot and 150 on the tesla arc slot. I've got some funding left so what I'm gonna do last is throw a Limiter Override console into the cockpit and specifically leave it powered down. Powered down consoles use no energy but their functions can't be accessed in this state and it takes a turn or two for them to boot up once powered.
And thats a rough idea of what building a mech would be like, obviously with numbers just made up off the top of my head and a lot of stuff abstracted or assumed. Still, it gives you an idea how it will function. I'll probably do a little showing of how it behaves in combat next....