Talking about server administration and security but not knowing about bandwidth is a bad thing..
768kbps should give you about 96kB/s of downstream client-side.
However you might have a cap per-client and not even know about it.
But then if you were downloading from a 512kbps connection, doh.
I'd say that you'll be attacked by a spider and not by someone willing to take out data from your server... Unless you've gave them a reason for said action. In that case you should have a simple reaction: block their route.
Talking about spiders, how lame can people be this days? They are concerned about spiders stealing their email addresses, so what do they do? put an image with their email address.. Cool, jerk, you still got your email on the mailto: - You are avoiding nothing then!. They dont realize thats where a spider looks at... So thats why the purpose is to put an image with out any link. Even though you could still manage to catch the address from the image with some simple algorithms, however who the hell you think you are anyway?

- No one cares about your email address that much exept for your own self!.
Running a bunch of services is something that even my dog can do.. Administrate them correctly in an efficient and professional way, is something you'll only be able to achive after many years of experience on server administration.
Log analyzing is a good routine anyway. You dont only get to know about possible attacks attempts, you'll also check out referers (important, you want to know whos linking to you for example) and even download counts for the heck of it, in fact you can analyze bandwidth used per directory, or anything you'd like to analyze.. Logs are very important. Something that really annoys me is how many of this little kiddie hosting "companies" (well they just bought a reseller plan, they dont own any servers...) never provide said logs to their customers, in fact many of this services are as unsecure as going to a gay parade on shorts.
So yes, thats it. Wear a lock, a good brand one.
(meaning in this case: Keep an eye on your server if you're letting it out*).
* Inet access.
Now excuse me but I've got to go, see if it rains.