Unfortunately, there is no answer to this question. Different people have different ideas on this topic. Some people want everything to appear natural, and the tipping point for them is when their photos does not. Others couldn’t care less about that and in fact don’t want their pictures to appear natural. Neither approach is correct. So you are going to have to decide for yourself to a certain extent.
Once you decide on your general philosophy, that sets a range for you, but even then how you approach each picture is still ultimately up to you. I will offer two additional thoughts on this topic: one cautionary, and the other encouraging.
On the cautionary side, I will say that beginners are much more likely to overdo the processing than people that have been doing it for a while. They will end up with garish colors, or they contrast is too much, or they’ve pushed everything too far and generated a lot of noise, banding, or other effects. Although the HDR craze has largely faded (due largely to the ability of post processing software to pull detail from highlights and shadows without resorting to HDR), it used to be quite common to see beginners proudly displaying totally overdone HDR shots. So be careful when you are just starting out.
On the other hand, don’t let comparisons of your edited photo to the original hold you back. I am frequently guilty of this one. I gleefully edit away and then I go back and compare my edited photo to my original. When I do, I see how far I have come and inevitably decide I have overdone it. It doesn’t look like the original and that bothers me for some reason. But you have to keep in mind that nobody is going to see your original. All they see is the final edited picture. It will likely look just fine to them. Don’t let that hold you back.
All you can do is decide for yourself. To help that process along, look at others’ work and pay attention to whether you think it looks overprocessed or not. Go through a bunch of pictures on Flickr or 500px and I think you’ll pretty quickly be able to decide where you fall on the scale.