TGC has tiles similar to playing cards but thicker that measure 2x2". The standard size mat is 10x10". This would allow for slightly fewer than 5 tiles in each direction. These pieces informed a layout with 2 slots for each arm, 3 for each leg, 4 for the body, and 1 for the head. That makes a nice, even 10 slots.
Aside from the physical layout, I had ideas about other game mechanics that I think are novel and hopefully good. These involve the firing of weapons based on a hand of cards. The cards would be standard sized and numbered from 1 to 4. Each weapon is rated as to the number of cards that can be played for its attack and the maximum point value for each card. For example, a lowly machine gun allows up to 3 cards but only a value of 1 for each. The tough large laser on the other hand allows 4 cards with a max value of 3 each. The interesting mechanic is that when cards are used to fire, they go into the 'heat' pile. Heat tracking is a standard part of Battletech. It is a way to limit the amount of firing a mech can do; once the heat builds up, you can shut down or even eventually explode. By using the number of cards to track heat with each card having a maximum value, the weapons can be tweaked to set both their power and the amount of heat they generate.
With heat building up there has to be a way to dissipate it. This is handled by heat sinks. There is a default amount of heat (and therefore cards) removed each turn naturally, plus a mech can be built using slots for heat sinks to remove additional cards.
Another aspect to a weapon is its minimum and maximum range. Distance should be important, but with the game striving for simplicity I didn't want to have a board to move on. The compromise I thought of is just tracking the distance between mechs. At the beginning of each turn players can allocate cards for movement. The player who 'bets' higher gets to decide the new distance by using the old distance plus or minus up to the total of the move cards played. So if it's important to a player to use a particular weapon with a particular range, they can use up more of their cards to ensure that the distance matches the range.
So those are the basics that I thought of. The problem that I had trouble dealing with is exactly how it would be determined if a weapon hits. Having a deterministic weapon power versus armor strength mechanic seemed too easy to calculate the ideal with no variability. Dice seemed the natural answer. Since the total power (sum of cards played for that weapon) ranges from 1 to 12, a 12-sided die is perfect. In order to hit, the player rolls a number of dice for the strength of the weapon, and the target needed is the total of the attack cards played. For each die less than the target number, a hit is registered. Ones always hit. This seemed like a good compromise between a purely deterministic model and a very random one.
With these mechanics in place, the next step is to flesh out the details and attempt to reach game balance. It will be interesting in that players can choose pre-made mechs or create their own for an added level of strategy. I'll continue to play test myself and tweak these basic ideas. Then I will try it with other people. Oh, and there is the minor detail of seeing if the game is actually fun!