1)Since particularly the keyboard cord is about 2.5 feets long is there any possibility or RF interference to nearby welding going on. Do I need to use isolation for K/B and LCD as well. 2) Do I need separate supply for these devices and micro.
1) do not worry about the display, it is constantly refereshed and a "zip" on the display will not affect the function of the machine. The keyboard should not be a problem if the debounce is at the receiving end - being a cleaning lady I do not know - but if the debounce is in the keyboard add some debounce at the receiving end.
2) the above should take care of using one supply.

Erik