I'm not as knowledgeable as some others, but I'll try to help. First, I assume that was just a typo, and you meant NORTH not SOUTH.
If you head towards the Smokies, you will enter the national park almost immediately. The trail through the park is a little more than 70 miles long, ending at Fontana Dam. You have the option of ending sooner at either Newfound Gap (~30 miles) or Clingman's Dome (~40 miles). From I-40 it will be uphill pretty much all the way, or you could start at NFG or CD and walk north to I-40, which will be downhill. The park requires that you
obtain reservations for each shelter or campsite you intend to use, and carry a copy of the permit with you.
Heading north from I-40 is similar terrain, though more varied (both up and down), and without the hassle of permits. I think it's about 30 miles from I-40 to Hot Springs NC. To Allen Gap is just under 50 miles. Use
www.atdist.com to check other mileage options.
In either case, if you do this in mid-April of next year, the trail will probably be LOADED with thru-hikers. If you want company, you'll have it. If you want solitude, adjust your plans.
Also understand that mid-April weather can be pretty chilly. We did weekend trips in the Smokies in early and mid April and early May. For each of them, we dealt with temperatures in the teens at night. On the early May trip it was snowing lightly when we got back to our vehicle near Clingman's Dome. Or it could be warm, but be prepared either way.
Assuming you have good weather, you'll have beautiful scenery and great views regardless of which direction you choose.