There's nothing wrong with over-insulating (although at a certain point it is no longer economical), but you need to ensure the house is ventilated to prevent mold.
You also need to ensure you choose the correct building materials, so they can ventilate themselves. Modern building science says there should be a continuous airtight wrap around a house with insulation either side. The interior insulation ventilates to the inside, and the exterior ventilates to the outside. What you don't want is multiple airtight layers as that could cause it to become moldy inside the layers.
Passivhaus houses will almost always have a heat-recovery ventilation system. These will bring in fresh air and take out stale air - like a bathroom fan. But they also exchange heat from the outgoing to income air in the process. Typically 80%+ of the heat is recovered (you can get systems that are 95% efficient). They run at a low speed so consume minimal electricity (typically under 100W for small houses) and don't provide a noticeable draft like air conditioning or forced-air heating. They have filters to prevent pollen and other contaminants from entering your house, so for allergy suffers they are a big plus.
I live in a cold climate in an apartment built in 2015, which is well insulated and has this system. Even though it has been below freezing (currently 8c) outside, we haven't yet needed to turn on our heating because of how well the building is insulated. We do actually have a typical vented bathroom fan, but everything else (kitchen hood and dryer) are unvented, so we keep all that heat inside.
Where did you learn about modern building best-practices? I just bought my first single-family home and am excited to slowly transform it into a comfortable-and-efficient modern building. But I'm finding it a little difficult to penetrate this new-to-me space and would love to find some more-complete resources.
My random web-crawling has certainly been moderately productive, but it's slow and I can't help but feel that I'm not being adequately exposed to a reasonable breadth of topics.
