If you come early spring you may be dealing with high creek crossing from snow melt! There are really quite a few options in the Smokies and like Topshot said, keeping mileage manageable is way to do it. Don't try to push 15 miles in the Smokies for your first time (I can imagine 15 miles in Florida would be easier than here.), I'd say keep it around 6-8 miles a day with light as possible backpack, and you have all day to move that far. One option you should look into is maybe keep your first couple days long and final day short. For instance you're going to do a 3 day hike for 20 miles, on day one do 7 miles day two you will do 8, and final day will be easy 5 mile stroll to the car. Philosophy behind this: is day one be the ease your legs into the trail kind of day. Middle of the trip will be the gauntlet day of hardcore hiking, while final day when you're tired you'll have low mileages to the car and can take it easy. It's just something to consider when mapping out mileages when you get a route since if you do it hardcore on day one, you will probably be super tired the remaining of the trip. After all it's a marathon not a sprint!

Also, when reading trip reports online about difficulties in the Smokies, take it however you want. I ignore them (well, I do look at the sweet pictures!). Why? i can't tell you how many times i been day hiking and ran into exhausted tourists biting off more than they can chew. Why? They may walk several miles on a flat track while their kids are playing ball, or walk the dog down the street, walk around outside on their lunch break, etc., then think they could do a 4 miles 1,600 feet climb with no problem. They go and do it only to be in sheer exhaustion due to elevation and uneven terrain as well as factoring in pack weight. Therefore, that's extreme difficulties to them, where to me, a difficult trail in the Smokies is mostly long mileage. All of the climbs in the Smokies are tamed to me unless I carry an enormous pack weight which I have no intention of trying. I can do a 13 mile hike in 6 hours with less than 10 pounds on me. I've done 17 in a single day with 20 pound pack in about 8-9ish hours of walking time. And I've been doing this for quite a few years as well as riding mountain bikes regularly. When I go out west to the Rockies or Sierra i'm going to get my butt kick badly, and will be just like those tourists that come here once a year

If you have any specific questions regarding backpacking in this area, feel free to PM me. I can also help you with gear selections in this area if you want an input, and others here can help you get started as well. I've learned a lot from these folks on here. I might be hiking somewhere in Smokies when you decide to come up. I'm either in the Smokies or in western Carolina.