You need to find out, otherwise it’ll all stop working as soon as your router is reset or your connection otherwise drops for whatever reason. (And if you don’t know, chances are that it’s dynamic and this will be an issue). Something like DynDns might be a better option.
Personally, I wouldn’t do it. If you have to ask what the risks are, that’s reason enough to make it a bad idea. (-: But also bear in mind, you’re (presumably) sharing stuff upstream the wrong way along an ADSL connection; so anything you copy off externally will transfer at your considerably slower upload speeds. External hosting is usually a better idea, for this reason.
What are you trying to achieve?