Do I need to cycle or cross train to prevent overtraining?

No you do not - the UTC algorithm personalizes your ramp up settings depending on your running history, injury susceptibility, etc.

So if you want to build from running 6 hours a week to 10 hours a week, UTC will work out the increase in training load for you.

You don’t need to change planned runs with cross training on your own.

You can always cycle and swim a bit apart from your training schedule to loosen up and recover, as long as you keep the intensity low.

We do recommend you to add some strenght & conditioning - check out the tutorial videos in this respect. 

S&C training will have positive impact on performance whilst reducing risk of injuries.