I sort of see where you're coming from, but, honestly, it's not really D-Link's job to include a tutorial on every little basic configuration scenario like this that a user might encounter.
Furthermore, there's absolutely nothing proprietary or different about the DNS-323's standard FTP server than any other FTP server (the FTP SSL that they incorporated in the latest firmware might be another story), so you could just Google any old tutorial about setting up a home FTP server to accomplish this with the DNS-323.
It's sort of like saying car manufacturers should include instructions in the owner's manual on how to steer the car left and right, but, since it's been the same for just about every car made in the last 100 years, it's just understood.
But to answer your questions:
1. No, but it does help since you won't have to remember your IP address, nor will you have to worry about it changing. www.dyndns.org is one of the more popular ones and is free to use for basic dynamic domain names.
2. No, however, they may be blocking the standard FTP port, 21, in which case you'll have to port foward a different incoming port through your firewall, which is a good practice anyway, as it might be a first line of defense against people just perusing for servers responding to port 21 requests.
Lastly, just download a free FTP client, like Filezilla for PC or Cyberduck for Mac OS to access your FTP. You can create a favorite in each, so you don't have a username/password just sitting out there in your web browser history or in a browser bookmark.