You don't need interrupts to read your sensors every 250ms. Look at the Blink Without Delay example in the IDE (File->examples->02.digital->Blink Without Delay) to see how to track elapsed time. Then, read this tutorial: Serial Input Basics - updated to see how to handle Serial input without waiting for an entire line to arrive before processing it.
After that, check this out: several things at the same time which explains how you can break things up to small things each time through loop()
As for your code, it is hard to comment since it is not a complete sketch and lacks import things like variable declarations, etc. It is very rarely (ever) a good idea to post code snippets.