The most obvious upgrade for me to the E-170 would be a sump for sure! :-)
A sump will increase your water volume a fair bit, and give you better room for additional equipment such as a good protein skimmer (Deltec dc-400)
I had a Reefer 170 running for a good couple of years with 2 x AI Nero 3 powerheads, that was plenty enough - and gave me good results!
Also, dejligt med endnu en Reefer fra Danmark! Velkommen om bord! :beaming-face-with-smiling-eyes: