I do have a static IP of sorts, not technically static though it will last for several days without me using it and then get provided to someone else. The big problem is that my ISP already assigns a hostname 203.51.8.6 = CPE-203-51-8-6.nsw.bigond.net.au (Yes I did falsify some of the IP for this example) so if I was to use DNS which hostname would work, mine or theirs?

I could upgrade to a static IP with no drama and a fixed annual fee though the same hostname issue applies, I am stuck with one provided by the ISP.