If you buy the "pushmail" app you can set up sound profiles for your email. And make it go silent at night. I don't know an easy way to turn off the text message sounds unfortunately, without doing it manually every day.
Easier? No. You can set pushmail to AUTOMATICALLY turn off notifications. For all people, a few, have different times for different days of the week...Wouldn't it just be easier to turn OFF push notifications at night? Why use a separate app for this?
Never though of that - turning off Cellular Data. Probably the easiest way. I don't want to install another app.
That won't disable all of your other notifications, (text, email if you're on wifi, ect.). If you go to settings->notifications you can disable everything from there, so that if you get a text, nothing will happen until you unlock your phone and read the message - no alert, notification center bar - nothing.