Some places require you have high limit auto and home/renters before they will provide umbrella, since umbrella kicks on top of those in the event of a loss. I agree with others, I would talk to an agent and explain you want non owners auto at least 100/300/100 BI/PD and renters w 500k liability and an umbrella with an additional 2 mil liability limit.

And when thinking of the amount of liability coverage I need, I would consider my own assets and likelihood of being sued and having to sell off assets in the event of a judgement against me. For example, if I live in an apartment that I rent with no savings or assets, I might not worry so much about getting sued, but if I had significant assets, owned my home, etc, I would worry more about the likelihood of me getting sued. If that makes sense.