Does anyone know what the line limit is on work orders?

AFAIK there aren't line limits that will actually stop you on any transactions in NetSuite, but eventually the performance degrades to the point where things stop working, so in reality you effectively do. SuiteAnswers 93870 and the related links will give you a sense of where those limits are. tl;dr if you're under 200 lines I think you'll be fine, but you'll want to test performance and make sure you're okay with how long things are taking to load.