If your VPN/SSH/any server will be on the OpenWrt or downstream of it, you still need a domain name so you don't have to remember the (changing) IP address.
OpenWrt offers a DDNS app for the web GUI. You can use whatever DDNS provider you wish.
- I use noip.com, they do 30 day renewals
- I also use HE.net's DNS service - it's free with no activity timeout; but you must purchase your own domain name