I live in Orlando and honestly haven't been around the state too much so I can't tell you about a whole lot of things to do here, other than the area I'm familiar with. A few ideas...
I'm going to throw out these ideas as if you were traveling from the Keys, North up the East coast of the state, and then head West across the state, then North again. The only part of the state you'll miss will be the Jacksonville/St. Augustine area. You could always go up, then come back. It's about an 1-1.5 hours from Daytona.
So, if you're starting in the Keys, head North and you'll come to:
The Everglades National Park. There was a lot more to see before people came around! lol
In that area is:
Tom Crutchfield's facility. As far as I know, he's usually willing to welcome visitors.
There are also some of the larger importers down there in the Miami area and I'm sure Tom could give you an idea of the better places to visit as I'm pretty sure they likely have a storefront.
Miami is known all over the world for its beautiful women (many of whom paid a doctor for their beauty) and its nightclubs! I haven't been, but from what I understand they don't wear much at the beach. I also understand that you can get Cuban cigars there - if that interests you. Food should be VERY good and a change of pace from the rest of your trip which will just be typical American food and seafood (until you get to New Orleans).
Slightly North of Miami is Ft. Lauderdale/Hollywood, FL. I'm not overly familiar with this area, but if you enjoy gambling, then be sure to visit the Hard Rock Seminole Casino in Hollywood, FL. It's ENORMOUS and VERY cool.
Further up the east coast (about 2 hours), there are two "must-see's" in Melbourne. The first is the Brevard Zoo. It's been improved lately (was fun before) and is larger with more exhibits. If you have kids, they have a great area for kids. If we have unseasonably warm weather, they have a great new kid water park! The highlight of this zoo (in my opinion) is the observation deck for the giraffe's where you get to feed them at their eye-level. Also, the bird exhibit is fun. You can feed the lorakeet's as they fly around all over the place and land on you
They've got a little petting farm area too with goats, etc..
The second stop is Incredible Pets in Melbourne. PHENOMENAL exotic pet store with great displays and some REALLY cool animals of all kinds.
You can take a gambling cruise out of the nearby port in Cocoa, FL. They'll go out for a few hours and swing back. It's free and so is the food. Don't know about alcohol being free or not as I don't drink. Heck, come to think of it, if you wanted to take a cruise, that's the perfect place to depart and head down to the Caribbean. Cruise lines are practically GIVING AWAY cruises to the Caribbean. I've heard of 3-5 days cruises for VERY MINIMAL money. Could be a fun diversion from your Florida based vacation for a few days.
North of Cocoa and Cocoa Beach is Daytona.
Daytona isn't one of my favorite places. Very run down. Also, depending on when you're going to be here, the Daytona 500 will be taking place. I just looked it up, it's February 20th, 2011. That could be a pretty cool experience actually. Avoid Daytona during March 4-11th this year, it's bike week and the traffic is horrible. Unless you like motorcycles - then, GO!!!! From Daytona, you can hop on Interstate 4 and be in Orlando in 1 hour.
If you don't want to go to Daytona, then at Cocoa, FL (gambling cruises I mentioned and just north of Melbourne where the zoo and exotic pet store is), you can head West towards Orlando on State Road 528. Depending on where you're going in Orlando, it's about a 45 minute drive to your destination.
In Orlando, there is a TON of stuff to do.
It's pretty short on reptiles other than the St. Cloud Serpentarium (small place and I haven't been in 10 years, but it's pretty cool and they have venomous). But, there is:
Disney World (4 parks plus 2 water parks which may be too cold to visit)
Universal Studios/Islands of Adventure (my 2 favorite parks)
Sea World (how can you pass up Sea World???? - another great park)
All three of these places are relatively close to each other - only about 20-25 minutes apart from the parking lot of Universal Studios/IOA to Disney - with Sea World in the middle of that 25 minute trip.
If you like Roller Coasters and you're just choosing one destination, go to Universal Studios and Islands of Adventure (two parks right next to each other). If you want an animal experience, Sea World is a good choice, or Animal Kingdom at Disney - the choice is dependent upon whether you want aquatic animals or not. If you choose Sea World, you can buy a 2-park pass and go to:
Busch Gardens in Tampa. This is a great place for animals AND roller coasters. Because you're going this way anyway. It's about an hour West of Orlando on Interstate 4.
All of the theme parks should be relatively slow in February until Spring Break starts. Even then, they shouldn't be PACKED.
Feel free to bring a nice camera to any of these parks if you don't mind carrying it around all day. If you decide to ride a roller coaster, etc., they'll have lockers you can rent (sometimes free) to store anything you're carrying with you.
From Tampa/Busch Gardens, you could drive North up the Gulf Coast of Florida.
South of Tampa (the opposite direction you're driving) there's not much to see. The only thing you'll miss out on is Alligator Alley which is pretty boring anyway unless you run over an alligator or feral pig, which will ruin you day. There are some nice beaches (Sanibel Island, Marco Island, etc.) but if you're going to be in the Keys, they wouldn't be much different. So don't worry about missing them.
After that, I don't know what there is to do here in FL. Sad... I know. I'm not a very good ambassador for the state 
Depending on your time frame and what you want to do, you could always head up to Atlanta, Georgia on your way to New Orleans. Atlanta is a HUGE city (5.5 million people in the greater metro area) and I'm sure there's no shortage of things to do there. A few hours north of Atlanta is the start of the Blue Ridge Parkway. Probably not much for a German tourist to see in the mountains and you'd likely rather stay away from the cold weather! lol But it's an option.
If you enjoy good food, New Orleans will be a NICE treat for you. I've only been once, but I haven't had food that good before, or since.
Pack warm and cold weather clothing. You'll encounter both on your trip! Good luck!
jb
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What's written above is purely my opinion. In fact, MOST of what you read on the internet is someone's opinion. Don't take it too seriously 
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