Can we work any hours and with any employer during OPT period or just stick to only one wmployer and related with study only. Pease advise if anyone is working or has an experience? Any chance of being illegal while doing so??

You can work any number of hours and for anyone as long as your OPT is valid. As long as I know, you will not be illegal/out of status. However, do double check it.

Since there is no employer's name and working hour are not written on Work Authorization Card, you should be fine to work. But still check with experts. I also could not find anywhere written during OPT you must stick to one employer just like in H1B. Ask with your international school indirectly if possible but they will definitely say you can not work.

you can work anywher within USA, as much as you want and get paid as much as your employer wants during your OPT period.

May be you can work at WalMart and other Grocery Stores for additional hours with your card. Try your luck.................