Well if you just started using Pyrrha, just keep in mind that she has some of the best Oki in the game and for the most part is very safe. You can get pretty far using just BB and AA, and then just experiment with other pokes after knockdown. 1K is probably her best low poke, and 3A+B is a...
I know if you get a stun with Omega, like 4B or WR B then you can just G, 9 and then hit B+K. I don't think Pyrrha has any practical ones other than like Violent Vodka said maybe CH 6K.
That's her BT B+K. You can do one after 33B, but that's pretty much the only time it's guaranteed. It has pretty good ring out range, but other than that it isn't overly useful in combos. It is a pretty good back turned interrupt though.
If you can tell that it is going to be a NH 33B, then bA does more damage, as well as having much more range, so it won't whiff at max range like twister will on smaller characters if you JF it. It also gives a much more desirable knockdown for a better Oki game. Plus you get extra style points.
You should not have very much trouble dealing with backstep at all with aPat, as he has arguably the best backstep kill move in the game with 2363B. It's one of the only moves that can even catch Nightmare's backstep fairly consistently from mid range. Not to mention this is my personal pick for...
By far the best option after guard break is to try and land a GS B, because GS B > GS B > GS K (BE) is huge damage for just one bar and rings out from massive range. If their guard is red, using moves 22A into GS or 66K into GS are good ways to try and fish for it, but it might get kind of...
6A+B is by far Maxi's best move, and one of the best moves in the game. Tech crouches, decent range, safe on block, catches sidestep, mid that knocks down, and super fast (16 frames?). Don't be afraid to throw this move out A LOT, because it's good for both punishing and doing basic mixup. You...
For BE bullrush you can JG the second hit and punish for big damage. Standard bull rush is really hard to deal with. You can GI and sometimes you can sidestep it. Other than that it's usually best just to block. For the fully charged version, options are very limited because it has huge range...