Benimaru is a pain in the ass, you can't anti air him, but because you are that small you must always guard crossup so it's kinda predictible.
His far D is unbeatable, if you have good reflex you can ex throw/qcf hcb.BD him but ...
The best option is to predict it and jump over and then hit him with the dive kick, if you are far enough you can zone him with your fireballs.
On the demon flip mixup after a s.B blockstring he's quite free because if he dp your demon flip he will whiff, so he has only two options : guard or jump, guard can be tricky and difficult depending on the dive timing (forward*2, backward forward, backward*2), the jump is beaten by the throw and the roll by an option select sweep on the dive.
So if you land one dive go for the maximum damage and kill him as soon as possible (It's quite easy to hd off of it so don't hesitate).
Leona has every d~u.P/K anti air forget cross ups mind game and go for a throw/d.B mind game.
Don't jump/Saifa/Fireball against her.
Takuma is the most stressing char of this game be patient and cautious, if you're in corner jump only if you fell a throw attempt, jump CD his a combo starter for him ...
His fireball game is good but you can charge your meter without letting him to do so by using saifa, plus your kohoken stay still against his projectile and has more range than the qcf.K of takuma.
You must jump against him, it's his weakness, but only hops/superhops, because his Ranbu will beat any of your jump/hyper jump attempt, if you don't have thrown an air fireball. Use and abuse of your divekick.
Karate ... well I don't know. On his pressing (lights to f.A to qcf.P) you must block there is no real weakness (break cd is beaten, break roll will only permit you to go out of corner) because this thing is toooooooo safe.
Don't jump/hyper jump against him, good dp. but like takuma you can use your dive kick if you're cautious enough. You have also a good throw game. Don't try to anti air him, he's too fast, guard.
For both takuma and karate be very cautious of the cross up D.