Traveling Alone to Europe [closed]

I am planning a solo trip to Europe. I am a U.S passport holder and have an additional non-U.S. passport. I've never traveled by myself and have some questions. Also, the countries I plan to see are Belgium, Germany and Netherlands.

Question one, I plan to rent a car in Frankfurt. Are there any potential required insurance charges beyond the final pricing shown on a site like Expedia.com? I've rented cars in the US previously, and wasn't required to pay for additional insurance. I'm not sure if car renting in Europe is different.

Second, are there any special consideration regarding driving from one country to the next as far as crossing borders?

Third, I plan to arrive there sometime at the end of December. Is the weather manageable for tourism? What is the best course of action for packing to ensure an enjoyable time and a good level of comfort when walking the streets throughout the day?

Lastly, I'd like to make friends on the way. Does anyone have experience with couch-surfing to find travel friends? I basically want a quick and hassle-free way to meet up with friendly fellow travellers and/or locals.