There are several moths that visit cote crops. The most common in home gardens are the cabbageworm.

At this point in the season, you should physically remove the caterpillars that you find on the cabbage. You can also use row covers to prevent moths from laying new eggs. They all have several generations each year so row covers will help.

Your cabbage heads still look really healthy and don’t show and signs of mites.

https://extension.umn.edu/yard-and-garden-insects/caterpillars-cole-crops

What if I'm not seeing any caterpillars?

Can I use row covers on those two heads or is it to late for them?

That is a caterpillar in your 3rd photo.

Yes. Put the row covers on.

Oh ok. Thank you. I thought that was bird poop.

Should I still get a pesticide spray and spray the plants?

It could be bird poop but in the photo it looked like a caterpillar. Your cabbage shows some feeding damage but overall looks pretty healthy. 

I would pick off any caterpillars you see and drop them in soapy water. When you harvest, remove any parts that have bird poop or any other kind of feces. 

The 5 gallon buckets are fine. I would not spray them with anything. They are fine to eat.

https://extension.umn.edu/yard-and-garden-insects/caterpillars-cole-crops