Modern fobs should be designed to prevent replay attacks (there should be something specific in the request that alters the response), so it shouldn't be possible to record a response and then use it later.
Or money quickly loses all value. What do I care if you give me a million dollars? It'll be gone tomorrow, and until then everyone else will view it as being just as worthless as I do.
Possessions you have control over at the beginning of the day would matter (so yes, being rich is still an advantage), but I imagine any intangible funds would be worthless.
I assume it depends whether the urine is still imbued with the speed force long enough to run down the drain before it can be flung away. I'm not sure; I'm not really an expert in speedster physics.
I believe that "a" is either "a" or "an"; it depends.