Very cool! It looks like it was printed with those lines.

Is it in a humid area with low air flow? Powdery Mildew is tough to get rid of and very easy to spread. You can try diluted hydrogen peroxide spray, neem oil, fungicide, etc but getting rid of Powdery Mildew is an uphill battle.

Did you end up saving this pine? I tend to not give up on plants which sometimes doesn’t work out, but I’m curious what you decided to do!

They shouldn’t hurt it.Mushrooms are growing because spores made it into your potting mix and the conditions are right. It has more to do with the soil vs the plant, but some say it can be beneficial to the plant. At the very least it shouldn’t cause harm and you can remove the mushrooms if you don’t like them. If you want any to get rid of them, repot into a new medium.

Looks like Edema. Here is a good explanation of what is happening YouTube Video

How much bitters did you put in the batch? I love bitters and would love to try this!