> how would the installer work, would you select some options and then the > installer would download those files online and install them or would we > provide separate installers for each option? In any case, how do we need > to supply those files, can we have them on a ftp-server or would a > web-server work too?
Yes, it is possible to download the optional components from a web-server. Though it is best to avoid it (user firewalls could block the installer, connection settings could be non-standard).
> Also how much work will it be to create and maintain those installers.
Creating the installer is really not much work at all, nor is updating it. Deciding what to include seems to consume way more time ;-).