American Working in Mannheim - Where to live? (Frankfurt)

I have been offered a job with my company to do a 2 year expat assignment in Germany. My office will be in Mannheim, pretty close to the train station. I expect to do a fair amount of travel for my company (25%-50%). I would suspect it would be split evenly between train and air. I'm struggling with where to live as I have not had a chance to visit the area yet, but will in a few weeks. I want to live in a metropolitan area, as much as possible. I have been guided by my company to Mannheim, Heidelberg, or Frankfurt. Now, to the best of my knowledge if I live in Frankfurt it would probably be best to take the train in to Mannheim.

I am a 32 year old single male with no kids and my company has allotted me Protected content to pay for a furnished apartment. They have also given me a car to use. Some things that are important to me are:
Local shopping and grocery
Night life
Younger community
Local Gym to exercise
Soccer
Bicycle and running paths
Easy access to train station
Easy access to airport

I have two questions for the experts here. First, based on my job location and the travel I will be doing, where do you suggest I live? Second, is Protected content enough for a 2 bedroom furnished apartment? FYI – I want 2 bedrooms because I want to setup a home office and have a place for visitors to stay. Finally, I would appreciate any other advice!

Thank you and I hope you all have a nice holiday!