Hitch for bike rack, revisited

First off, I am a brand new Prius owner and new to the forum, so I apologize if my question is redundant. I have searched for posts on bike racks, but most only discuss which brand to buy.

1. I am freaked out by Toyota's warning against hitches and hitch-mounted racks. My Prius is brand new and I don't want to do anything that would harm it. I understand that Prii are not made for towing, but why would a bike rack matter? Will I really ruin the car by using a hitch rack?

2. I already have a rack from Thule, which weighs about 30 lbs empty. My bikes together have a combined weight of ~ 50 lbs, if that. Other than the max weight capacity of the hitch, do I have to be concerned for a max weight on the rear of the car?

I'm going to be traveling cross country and dearly want to take my bikes. Rooftop is out because of the obvious gas mileage impact on such a long trip.

Any information, reassurance, or advice would be greatly appreciated. Be nice, please. And thank you!!