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This article will help:
https://www.gardeningknowhow.com/plant-problems/pests/root-eating-insects-identifying-vegetable-root-maggots-and-root-maggot-control.htm

Are you sure thay didn't look more like small flies? They are most likely cabbage root flies, which lay their eggs and the larva feed on the plants. Here is more info: https://www.gardeningknowhow.com/edible/vegetables/cabbage/control-cabbage-maggot.htm

To prevent worms from burrowing into the heads, try placing the entire head in pantyhose or other suitable nylon stocking until ready for harvesting. This is often done when the worms/butterflies are most prevalent, in spring and summer.

If the soil is acidic, then apply lime during the soil planting preparation. However, if you need to add lime, do so several weeks before planting. This will ensure that the lime has been incorporated into the soil and prevents damage to your cabbage seedlings. While lime is lime for the most part, that which is targeted towards horticultural use is usually preferable.

For the tomatoes, here is an article that you may find helpful: https://www.gardeningknowhow.com/edible/vegetables/tomato/early-blight-alternaria-tomato-leaf-spots-yellow-leaves.htm

It is ready to harvest once the cabbage heads reach full size (between 6-12 inches in size) but before it begins to split open. For more info on growing cabbage, this article will help: https://www.gardeningknowhow.com/edible/vegetables/cabbage/growing-cabbage.htm

I've only tried it once, since I have to grow in containers, but it was ready in late September. (I'm in zone 6b.) You're in for a treat. Those suckers get massive as they grow. I couldn't believe the size of the outside leave. Enjoy the process. Time will take care of itself.