this is one for the compulsively orderly.
Build a company sized force that is fairly well balanced and effective...
except that all units must share the same introduction year. not a range of years, the same year.
Like, for example, you choose 3055. All the units in your force need to have begun production in 3055. (this is ONLY an example) Not one year earlier, or one year later.
So, Pick a year from the Battletech Timeline, and build yourself a viable, even effective, force to the best combination of flexibility, battle-value, and so on, but you have to equip everything in that force with equipment that began production in that year, and no later.
and no later variants, either.