The 9M's extra weapons work pretty neatly, IMO. With three ERPPCs, you're going 5 heat over, but dropping one leaves you with 10 extra, and incidentally the support weapons generate exactly that much heat. Meaning, if you're in range for whatever reason, you can keep using your heat capacity effectively. Or you can fire all PPCs and extra weapons, yet dropping one PPC next turn cools you enough anyway. This works well with increases speed as well, you generate enough heat to hit the first movement penalty but you drop only to 3/5.
The weapon choices may not be the most optimal, we'll chalk that to newtechitis, but all in all, it could be worse. Like having two tons of Streak ammo, as so many 3050s upgrades are fond of doing.
As it is, the ammo placement is pretty smart. A lot of armor (half again as much as in an arm), can't TAC it under standard rules, and if you stand behind a hill, your leg can't be hit at all. Since the 'Mech has XLFE, you'll be out of play after an ammo hit almost certainly anyway, no matter which hit location.