Firstly, the logo has to go with this 2 backgrounds:
About the dimension, just make it as big as you want but make sure the proportion is right cause I'm putting it on the header, replacing the current logo.
Now about the logo:
It would be great/plus point if the logo has a vector art of me, something like this
You can find my pictures on my facebook, just add me
But its up to you, you're the designer.
I don't really have any other directions, just be as creative as you can be. Maybe I'll just give you some keywords to help you get started:
Money, Cash, Spend, Shopping, make money, personal, paycheck, marketing.
Oh, one more thing. The winning entry also have to give the logo in PSD format, with a white/ transparent background.
Good luck and start designing!