You're going to want a pad or stick if you are going to become serious about this game. Keyboard has too much of a curve to learn it. To answer a few questions:
TK8 flametounge moves you directly up when you do the flametounge; you should land right where you started after the little jump. TK7 will move you back a little, just as TK9 moves you forward.
A BnB is a 'Bread n' Butter,' basically meaning a standard combo. The combo you mentioned in your own post is one of V Akiha's BnBs. (A simple one, of course.)
About OTG combos, make sure you get your target down with an untechable knockdown. (623B, 2C, or j.C for example.) After the knockdown, it sometimes helps to dash in, then start the 2A mashfest. Make sure you don't pause in between 2As, that may give your opponent a chance to tech out of the OTG.
228 takes some getting used to. I personally don't play the keyboard, so I have no idea how it does with any TK moves. (I heard it's easier on keyboard, but I have no idea.)
As for combos you should learn, the mid-screen momiji loop is always useful, so practice:
2A (5B) 5C 4C 2C 623C (pause) 2C 623B 2C 623B 228B/C
That will put your enemy in the corner, and in a flamepit from anywhere on the screen. As long as you have enough meter for the initial 623C, the rest of the combo should build you up enough to do the Ex-Flamepit.
Other than that, get the Momiji loop down pat, and learn her OTG combos, as both are vital to playing her.