How do you make the difference between safe fermentation/mould and spoiled food?

Of course nose and tongue are indicators, but I would like to know more... without reaching spoiling or unhealthy stages.

I would like to preserve with fermentation and fungus, and I have NO FRIDGE by choice.

At the moment I buy sauerkraut. When I keep the jar a few days, some white fungus are developing.
Is it still safe?

I have bought some other lacto-fermented veggies like grated carrots, etc, and many times, the lid has been put over a piece of food, and it was not air tight.
=> the result is a more acid taste... it can even be fizzy, picking the tongue like cider!
Is it still edible?

I have bought a fermented goat cheese, and now I keep adding fresh cheese into my inox box (with an inox lid).
inox... I mean stainless steel, so much quicker!
I eat was has become transformed = creamy.
should I mix it or just scrap the surface ?
Is there a mistake I should avoid not to spoil my cheese?