Wow, thank you for all the input!
I have had to defer it for now, at least until next month. I don't live in the house any more, though I still have control over it (100% ownership). In fact, I live quite far away, unfortunately, but things change, life isn't always as predictable as you like.
In this region, hardly anyone use air condition units in private homes, as the temperature rarely gets over 80F. But when it does, it is often with quite some humidity, and as there are usually no air conditions installed in private homes, you sweat it out, literally, or use simple fans, open windows and so on.
I am thinking that just removing some of the moisture would bring it a long way.
Yet when I got to the house last week, the RH was only around 30%, so not yet the time of year for dehumidification!
Thank you, AC_Hacker for the kind words. For sure, this is a big hack I am doing, and I cannot wait to get it working. I will have to focus to get it up and running, and when it does, there will be an interactive website to explain all the systems, as well as historical data to document it.
I have just found that the house is currently using more heating energy than average in this neighbourhood. There are around 100 similar houses, and the annual use varies from around 5.5 to 18.5 mWh - and mine is around 14.5, while the average is around 11.5. This is despite me changing all the glass in the windows, and insulating the foundation in a very efficient way, as you can see in the video at the bottom of this post.
The control of the radiant floor heating is not easy to manage, I haven't yet been able to make it work, so most of the winter it's running way too hot - and I guess that's why the house is using more than average.
By the time I get solar panels, insulated where it matters and all the heat storage is up and running, the house will only be using a few mWh of heating annually.
Speaking of hacking, the video below is made using a hack of a simple thermo camera (with a video output port), a bullet wide angle camera, and both go into a small digital video recorder. I wanted to make it PiP but the formats didn't work together, so instead it's side by side. Total price of this setup for making "Video Thermography" is around 4,000 USD. I have had this for several years now, and maybe there are cheaper options available today. Otherwise, thermography cameras that do video are 10,000 USD or more, for what I know of.
If anyone wants to see the setup of the video thermography hack, I'd be happy to show it.
Until 0:26 in the video, you are looking at a foundation of a similar house, but original, without the insulation modification. From 0:26 to 0:39, you see the foundation which I have insulated on the outside. There are two layers of non-compressive styrofoam arranged to minimize gaps. The top is sloping around 45 degrees so water and dirt will run off, and the bottom is extending quite far into the earth.
On the side of the house (as seen in the video), it extends about 4 foot down, while on the back of the house (see the other videos), it goes down, then out, then down again. The thickness it 2 x 100mm, which is about the same as 2 x 4 inch.
Finally, it's covered in a mesh and then finished off with some strong concrete to make it flush. The bricklayer was a bit sceptical of my hack, but after he saw the end result, he was quite pleased with the aesthetic looks.