Welcome aboard Sean,
I own the same kit. Love it. Nice choice on bikes. I also have a Schwinn.
I also recommend heavier gage spokes or a stronger wheel. My spokes lasted 160 miles before they started breaking. Fatigue, time and poor quality Chineese spokes are working against you. Granted... I'm a big guy at 250lbs but it shut my bike down only weeks after I put it together... only to wait for weeks to get parts and put it back in running condition. It's only a matter of time. A stronger spoke or wheel will give you peace of mind and keep you riding.
I went to 12 gage spokes on my wheel. I ordered a cheap 12 gage spoke wheel from bikepartsusa.com for about $50. When I got it I tried mounting the wheel but found I needed a really large tire to fit the rim. I wanted to stick with off-the-shelf tires so I stripped the spokes off of the wheel I bought and used them to replace the cheap spokes on my Schwinn wheel. It took a couple of nights to do it but it came out great and it's a rock solid back wheel now.
Now... I've never re-laced a wheel with new spokes before. That got me pretty nervous. And the new 12 gage spokes didn't fit through the holes on my wheel so I had to drill all of them just a bit bigger to fit the spokes. But there is an EXCELLENT set of videos on YouTube that walk you through re-lacing a wheel and I just sat there and worked through it along with the videos.
Your other option is just to bring it to a bike shop and let them do what you need. But I swear by the 12 gage spokes. They are RUGGED and once the plastic GEBE pulley is snapped onto the larger spokes it stays put! It did not grab the 14 gage Schwinn spokes nearly as tight and could be moved around on those a lot easier. I didn't much like that. Some people have taken to using an assortment of glues and other methods to assure that the pulley doesn't move around on their spokes after they get it centered. That concern just isn't there with 12 gage spokes.
As far as centering the pulley on the wheel, after you snap it on, flip your bike upside down, mount your wheel and spin it. If you find some high or low spots on the pulley just bump it with your hand or tap it with a plastic hammer. Spin it again... and tap it again... until it is as true as you can get it. That will be true enough.
You will know if the pulley isn't centered by observing the belt tensioner. It should stay pretty still as the wheel turns. You can walk the bike down the driveway while observing the belt tensioner. If it moves back and forth then the pulley isn't centered on the wheel and it needs attention. A little movement is not that big a deal but over time it will fatigue the tensioner spring and the spring will break. I carry a spare but once I centered the pulley, the tensioner doesn't move at all.
I use my bike to commute to work every day... about 16 miles round trip. I have about 850 miles on it now and it runs great. I ride exclusively on pavement and the tires still look new. If you plan to ride like I do I recommend the following...
Slime in the tubes (Walmart)
A better kick stand to hold your bike up straight (Amazon.com)
A descent headlight and tail light. (Walmart)
You've got the fenders... that's good.
An Optima Fuel Bottle (Amazon.com) for extra fuel.
A descent riding helmet... safety first (Amazon.com)
Riding gloves... again for safety (I use work gloves from Home Depot)
A bike computer (speed/distance) (Walmart or Amazon)
Small tool bag and assorted tools.
A spare belt (GEBE) and a spare tensioner spring (local hardware store)
and lastly... a better bicycle seat. I got a cloud 9 (Amazon)
See how much information you can get from a total stranger that would rather tell you this stuff that get back to work on his real job.
Gotta love the forum.
One last time... beef up the wheel. You'll do it sooner or later anyway... might as well be sooner so you don't have to worry about it.
Below is a link to my blog "First Ride"...
http://www.motoredbikes.com/showthread.php?t=12728
Happy riding!!! Welcome aboard!!!
Ross in New Hampshire