I write, eat, and use mouse left handed and do literally everything else right handed. It is pretty rough sometimes but I like to think it doesn't limit my performance in P99. I do curse myself though for lining up my mouse on the left side of my comp first time I used it when I was a youngster.
I bought a left handed mouse and hated it, now I have a Roccat Savu which is sort of a neutral balanced mouse, it's not super inverted or curved for righties and it works well for me.
As for keyboard I use the Arrow Keys to move and then 6 buttons Ins/Del/end/ etc above arrows for 1/6 hot key, with keypad and other keys around for other important buttons. It's something like this but this isn't exact, actually Ins. is jump i think and Del is auto attack but can't remember:
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There's a lot of other ways to do it but this is just what is comfortable for me. It transitions well for other games too but its always annoying setting up keybinds and figuring out what's important and adjusting it as you learn a new game.