I'm new to cycling and have a Trek 7300FX hybrid that I've been riding, but it's too small (the salesman at the LBS didn't seem to care about getting me a properly sized bike) and I've decided that I want a road bike instead.

I was recently given a 1981 Schwinn World Sport by a friend who had stopped using it. He'd kept it out on his front porch for quite a while and the chain and gears are all rusted out. It has Suntour derailleurs (Honor RD, Spirit FD) which look all right and were working fine the last time he rode the bike as far as I know.

I'm considering tearing the entire thing apart and rebuilding it with all modern components because I want a beater bike that I don't have to worry about being stolen or being out in the weather, but also one with plenty of gears that shifts smoothly. The frame is in great condition except for chips and scratches in the paint that have a little rust, but I'm planning on sanding it down and spray painting it anyway. Additionally, I'd like to replace the headset to use a threadless stem and get rid of the quill stem.

Does this seem feasible and financially reasonable or should I just donate it to the local bike coop and try to find a good deal on a newer used road bike? I should add that I also like the idea of building the bike up from scratch to get some hands-on experience with bicycle mechanics. I'll mainly use the bike as a commuter/errand-runner and also to try to get into better shape so that I can justify spending a decent amount of money on a good road bike later if I decide to get more serious about cycling.