All the ICs are LS ones and there are ten ICs in total. Now please let me know. Thanks.No, 6V are too much. Check your ICs inscription. Which series are they? For example, is it an 74LS32 or an 74HC42? Check this out http://en.wikipedia.org/wiki/7400_series for details.
It makes a difference in tolerances and power consumption.
About the power supply, the manufacturers suggest 4.75 to 5.25V, but 4.5V often work in small projects. How many ICs do you have in total?