How many methane wagons and heavy grunts would you say are enough for a rush? I've always liked him and would just spam fodder, heavy grunts and his heroes.
I think a good reason he is not be played is due to his very weak early game. In the previous patch (maybe 2) he has no answer for rushes and will almost lose to any rush because he does not have suicidal grunts. That and he is a odd leader to play as considering leader powers are concerned. He may still suffer from a weak early game in this patch but don't quote me as I have yet to face yap in recent days.
I'll try forgetting about his heroes and adding more methane wagons to the mix.
I wouldn't waste the energy and supplies on his heroes on tier 1 unless on very rare occasions. The number depends on what the other player is running. If he is running pure marines it's tricky because the marines can destroy the wagons pretty quick. Maybe 3 is a good number and you keep it slightly behind the heavy grunts to give them their buff to kill the marines fast. If they have mixed marines and flamers it's good to have 3 or 4 meth wagons in the face of the flamethrowers, it debuffs them quite a bit. You can also make sure a dying wagon dies close to the enemy, as the explosion does pretty good damage. If the enemy is going with a spartan combo, you want to avoid the earliest engagement with him and have at least 3 or 4 wagons as well with the y stun ability on the heavy grunts, When he tries to jack a wagon, spam y from the meth wagons and the heavy grunts and you should be able to kill him before he jacks a wagon. In the very beginning cannon fodder can help in the earliest engagements but as the match progresses you want to have a higher quality army. If the enemy is spamming a lot of flamers, I like making some engis to compliment my army. Being able to expand through expos and minis is key as you build units. I like to upgrade infantry and get the heavy grunt stun upgrade to give me an edge to really control the map. If the enemy builds to many snipers, I build choppers and micro them accordingly during a fight to help remove the snipers. The turret drop and mines also helps with the pesky snipers.