Okay, so I'm thinking, since this is a tabletop rpg and not a vidya gaem, you don't need to have exact roles for the mechs - no need to limit the players to swords only, let them do that themselves. Let the game work around the player. So, tentative ideas for mechbuilding ahoy:
The following categories of parts:
Chassis: Pick one. Determines base strength, speed etc. Determines weight limit (and possibly number of slots, see below).
Armour: Heavy, determines level of protection afforded. 1 slot, possibly 1 slot per limb (for eg. heavy chassis coverage but lighter limbs to save weight)
Primary weapons: Big, bulky, impressive. Pistols don't really cut it, IMO. 1 large slot (hands) or 2 medium slots (arms).
Secondary weapons: Smaller, more things like rocket pods or even active sensor arrays. 2 slots (shoulders)
Powerplant: Either increases endurance (via more power accessible) or speed (more power = more powah to legs!). 1 slot.
External slot: Additional powerplants, maneuver jets (not flight units. If it can sustain flight it's a hovercraft with legs.) and other nice toys too big to go internally go here. Essentially a back slot. Probably subdivisable, I dunno.
Internal: Remaining tonnage. Additional ammo, abilities, etc.
Perhaps you're right and a more freeform system would be better, but I would still like to keep the different weight classifications in, perhaps we could have different parts for each weight, but maybe it could be condensed a bit, cut out the Micro and Titanic weights maybe?
Lemme chuck out my own idea to compare to your own.
Legs: The base of the mech, determines weight limit, ground speed, jumping ability
Chassis/Torso: Where the pilot sits, determines number of slots for computational and optical things? For some reason I feel like I want to avoid our mechs having heads.
Arms: This is where your weapons go, of course. I was thinking we could have two kinds of arms: one with hands for actually using weapons, or grappling, and ones with giant studded/spiked bits on the end for punching. I was also thinking, that, for weapons, each arm could have a max weight for weapons. Like, lets say we have two arms, both with a weight limit of 10 units. You could equip a weapon up to 10 units in each hand, but if you had a weapon that required 20 units, you could use it with both hands?
Secondary Weapons is a cool idea as you've presented it, perhaps the amount of these is determinable by the arms we equip.
Powerplant/Generator: Your idea is good and gives me this one: What if we just made it kind of an extra buff, like rings and stuff in MMOs, you might have a power core that boosts your computers, or legs, as you said, or we could make it a major boost that kind of determines the 'class' of your mech.
External Slot: This idea is pretty good as it. I dunno about additional power plants, but maneuvering jets for quick dashes on the ground, or maybe even extra storage for weapons, so we can switch in combat?
Internal: I've been thinking about this kind of thing all day. Additional ammo could be cool, also: what if it were possible to store explosives here?
So, I've been thinking about the way to handle Armor in this game. My plan is that each individual part has it's own armor and HP stats, and when HP hits zero, the part fails and has to be repaired.
Armor has stumped me though. I've seen it done so many ways in so many games. I want armor to be a thing you have to plan around, not a simple inconvenience, so when you're preparing for a mission, you think "Better bring some AP rounds" instead of "Ill just need to hit it a couple more times".
The best way to represent my idea, though up for debate, is having a flat damage reduction as armor. That way, little pistols and machineguns will bounce off the thicker armors, unless loaded with AP rounds, and snipers/explosives will have a role to play.
Tell me what you guys think of the ideas I've presented, and ill throw up a Google doc tonight to hopefully celebrate the first major decision we've made as a group.
EDIT: I also completely failed to transmit my vision of this game's seriousness.
Basically, I wanna do cool stuff, but in a serious way. One thing I really want to do is mech sized rocket hammers.
And robot fist fights, and wrestling, and tons of stuff. I want to see robots with swords, axes, machineguns, cannons, spears, lances, sniper rifles, gatling guns, flamethrowers, all sorts of awesome stuff.
Also, I realized the lore i've made for this game is complete ass and it needs work. I want to keep the world, but I want to figure out something better than a giant Planetside with mechs.
Also Also, names, we need to do better names. Plated Souls is okay, I guess, but I don't want to be the only opinion. The mechs right now are called Souls, but I don't know if that's a good idea either. Also, our world doesn't have a name at all. So suggestions, suggestions, suggestions.