KI-84 is uber. HTC should perk it.
Not really but man do I love that plane. It's a pretty dang good plane to fly in the 200-300 mph zone. But the key to winning against most planes in it is to try to keep the nose above the horizon. Now obviously if you need to dive under a BnZ attack, by all means do it. But when the fight starts to get into horizontal turns you need to be pointing the nose up. This climb with store up E in the form of alt while dropping your speed into the sweet slow speed to pop the flaps out and all of a sudden become a monster turner.
Shoot in short bursts. You have plenty ammo but those MGs have a high rate of fire. Your peashooters aren't useless either, I can knock two sometimes three planes out with those once out of cannons.
Don't dive after planes that are faster than you. You'll rip your wings off and at high speeds the KI84 gets sluggish handling. If you want to pursue, follow them in a shallow dive.
Look for me in that nice black skin with the red arrow. After spending the time to learn the KI84 proper I've gotten much better in other rides. It's such a great plane I recommend it to everyone.
Oh yeah, for fuel I don't know if you really need to bother with any funny tank burn order. Auto has done me just fine. I used to take 50% and the dts but now I usually just go 100%