If you have a look at the 'Critical Updates' section of the forum you will see a thread about this Update
It looks like many members have applied the update ok, but I would compare your hardware to some of the systems mentioned to check for any issues. Also, you should have an off system backup of your critical data 'just in case'.
Regarding the DDNS, my personal recommendation (and my own setup) is to create your DDNS on your router (with a free account and these generally offer at least one domain) and setup port forwarding to your NAS to access the web page and apps. In addition, (again my setup) a VPN is a good idea, using the XPE/DSM package. Have a look at this post, which outlines DDNS on the NAS and also VPN, as asked by another member