I've never done much with Samba[1], but with both that and ftp (sftp, preferably?) I can imagine you've got a fine line between making sure you're not opening too publically and (from one side of the Great Firewall, especially) also not raising too many flags to the curious people in authority, with their steely hand of control over what P2P encryption/off-shoring they like.
But getting a (pseudo-)static address is the necessary first step, so as well as the DDNS hostnaming (may not be needed if you can get the number static enough for your purposes) you need to know that the 192.168/16 address won't be usable beyond your local router (or maybe one layer up, depending upon setup) and you'd need to use NAT (configure the internet-facing router/cable-modem to allow the relevent port-forwarding, probably) and then give your access-point's IP to the outside service/your contacts for as long as it doesn't get reassigned onward (maybe next time you power cycle and it has to renegotiate with the ISP - depending on exact setup in a whole complicated wkrld of possibilities).
All doable, I'm sure, just raising all this in case you aren't already aware, to save disappointment later when the project-creel reveals 'just one more thing' needs wrangling to get it working.
(Never worked with a DDNS, I'm imagining that it works by your system logging in to officially announce your current IP (by login packet source, assuming you've got the necessary NATting to work to make it useful) and adopt that as the current destination to resolve to by name-led visitors. Now I'm intrigued, though, wondering if there's a cleverer/smarter system.)
[1] A bit of autosetup, enough to get it working like a classic Windows Shared Folder, which always was a lot less tunable than most other networking setups (*nix, Novell, etc) but quick-and-dirty.