sure! There's nothing wrong with taking a year off.
You can take the OAT whenever you'd like, but since schools start taking apps in August/September, it's better to take it earlier in the application process than to wait until later in the winter, when there might not be any seats left at the schools you'd like to attend. I personally am taking it next May or June, since I plan to start applying in about a year. You also want to give yourself enough time to retake it, in case your scores aren't as high as you'd like them to be (I believe there's a 90 day waiting period to retake the test).