Meanwhile, I haven't been around on this forum for quite a while, does not mean I did not do anything.

Last improvement was the feedwater preheater that gave me a bit of fuel economy, and stretched the endurance of the feedwater supply by about 1/6th (350 ml feedwater initially lasted about 30 minutes, with installation of the preheater coil that stretched to 35 minutes...
AKA a feedwaterconsumption of about 600 ml/hr, give or take.

I found a suitable energy efficient centrifugal pump, intended for 12V but when powered by RX battery voltage, delivering precisely the flow I needed, at a very friendly 175 mA current draw.
I managed to install an additional cooling coil in the condenser body, and now I have full condensation and reclamation of exhaust steam.
Gone is the steam plume above the boat, and the result is that the boat now consumes less than 100 ml of feedwater per hour.

By now I have collected about 10 hrs of operational experience with full condensate reclamation, and all I can say it that it took quite a bit of research and experimenting, but it is absolutely worth it. Not because of operating cost or anything like that, but because of ease of operation: The boat now has a non-stop operating time of about 1 hour, and during that hour, the steam plant basically runs autonomous.

Unfortunately, no decent video yet. Only this small clip, where you can see that there is absolutely NO steamplume above the boat, meaning that all steam is being condensed back to water, led through an oilabsorbing filter, and being re-used.