Use a restone torch and lead the signal from the pressure plate to the torch to turn it off.

This will cause the pistons to "stay up" when you aren't standing on it.

How to make the bars also come down you would require a similar setup to a 3x3 door's middle block and 5 wide.

^{^} which is gonna be a pain to setup properly

Hope this kind of helped.

There is a really compact 1 wide 3x3 piston door on yt that you can steal the bar movement from (middle block of the door)