Thanks a lot for all of your replies!
We actually might be near Asheville at the end of our trip, but that depends on my relatives health issues right now. They are living in Columbus, NC. So Asheville would be a good stop, and we really dont want to go for tourist traps. Hiking will be on our schedule, so go shoot some ideas

I will definetley keep the change of Jacksonville to Cumberland in mind. That might really work for us.

The rental car price is actually okay, so we dont mind the one-way expense. I think we get quite good rates from Germany with our tour operator discounts.

We changed MB to Charleston. Thank you all for pointing that out! We might book a plantation tour and a boat trip.

For the Smokies we are looking for a decent place that can give us a little guidance, it doesnt have to be a cabin, we just go there to sleep and freshen up. We really want to go hiking and see some waterfalls, maybe a zipline tour and go somewhere with a good few over the mountains. My boyfriend loves to fish, but that might take too much time from our schedule.

We have been to Texas and South Florida a couple of times in August, but until now we just had a bit of rain and tropical heat. I hope we are lucky. We can cancel our Hotels 24hrs in advance with no fees, so If we fear it could get too dangerous, we will be thinking about changing the tour and maybe fly somewhere like Memphis, but that would be an emergency plan. But in the middle of hurricane season it's good to have options.

Thank you MissJ for all of your suggestions. We will definetly look up some indoor activities too, in case it really should rain or be stormy. We appreciate any suggestion about food and activities! We got the hotel part mostly covered.