Earthworms are good. However, adding compost and nitrogen is something you have to continually do. Compost helps build the soil web and nitrogen is very difficult to get enough of organically. Nitrogen is constantly changing and recycling so it needs to be constantly replaced. Planting inoculated legumes will help the next crop by fixing nitrogen.
Row covers only work if you can keep the bad bugs on the outside, it is a barrier. It still takes diligence and scouting regularly to take care of any issues early on. I have a garden full of lizards that like to eat beetles, caterpillars, earthworms, and mosquitoes so I don't have much issues with beetles. I have a different beetle problem Chinese rose beetles that like the same things as Japanese beetles. I actually use a Japanese beetle trap (floral lure) to trap them and I grow most of my roses under a street light and I only have minor leaf damage to my roses in the back yard that are not near a light. Since the lure of the trap is very effective, I locate the trap as far away from the target plants as possible. I have to take the floral lure out in the mornings and replace it after dark since the trap will also trap bees.
I don't have squash vine borer, but it looks like if you remove infested vines early and sanitize the area it helps. It also helps to grow other types of vines that they don't like instead. Unlike my beetles they are most active in the day.
There are commercial traps available
https://entnemdept.ufl.edu/creatures/veg ... _borer.htm
It is always a good idea to boost the garden patrol. Attract birds that like to feast on insects by providing habitat. I warn you though that some birds also love young seedlings so use the row covers. Grow nectar plants like alyssum, dill, fennel, carrot family (let it go to seed), sunflowers, achillea to attract beneficial insects
https://www.farmerfred.com/plants_that_a ... enefi.html
https://www.gardeners.com/how-to/attract ... /8103.html
It sounds like your soil was not balanced to start with. It is not just the mystery mix, but also that you were dependent on organic fertilizers and a new bed may not have a fully developed microbia to convert the fertilizer fast enough and the plants were probably deficient because of that. It takes years to build a good organic garden. Continually adding compost, and organic fertilizers. Nitrogen is really hard to get organically and the best sources will be animal sources like blood meal or scotts nature's choice organi lawn food. 11-2-2. You can add tomato tone or a balanced organic fertilizer like 10-10-10 or 8-8-8. You have to add it earlier than synthetics because it can take months or years before it is broken down and available to plants. fish emulsion, compost or manure tea would have to be supplemented weekly. Nitrogen is needed to get young plants to grow but it is also feeds the soil bacteria as they decompose organic matter. Your plants last year were starved nutritionally and so they were weak. Weak plants are better targets than healthy plants. Your garden should be better this year but you should add your organic fertilizers and compost 6-8 weeks before you plant so they have time to release their nutrients and once you plant out, feed the plants with fish emulsion weekly to grow strong plants.
Butternut squash, cucumbers, melons and watermelons are a different species of squash that SVB do not like as much.
I have all kinds of pests what we do is cover cucumbers, young gourds, bittermelon, and watermelons with newspaper or bags to keep them from being stung by fruit flies. Tomatoes get bagged too, not only from fruit flies but they need bird netting to keep the birds from going after the tomatoes. They especially like big tomatoes and small upright peppers. I like to grow large peppers that hang down, it makes it harder for the birds to get to them. Birds will go after small tomatoes but it is more productive so they don't get them all. Birds would rather go after the papaya anyway.
Bt takes care of caterpillars on the cucumbers and cabbages. Row covers may work for you. They hold too much heat for me so I use insect netting instead. Barriers only work if you have a good seal.
My garden patrol does most of the work so I do scouting and I have nectar plants and habitat to support them. I cut the hibiscus to control white flies and shoot water under the leaves of the peppers to keep white flies away from them. And I plant corn to attract purple lady bugs which really like to eat white flies. I put out ant bait to control aphids and scale. I still have problems with peach scale that is resistent to pesticides so I control that with a brush and soapy water, or if it is really bad, the plant gets culled. I have no good control for snails, so they are out of control despite all the sluggo I throw at them. I still go out early in the morning on snail hunts.
I rarely have to resort to chemicals, but if I do, I use the least toxic and most effective first.... alcohol.
I do get mites April-June on the hibiscus. Since, I don't want to get rid of the plant, I do disbud and use a short acting systemic on it. It is in a pot so it can be isolated.
Keeping plants growing as healthy as you can, scouting and controlling pests with the right method or just building the garden patrol up and giving them a chance to keep things under control helps a lot. Frankly the garden patrol does a better job of it. It is not 100% but damage will be tolerable. I definitely wish I had a couple of toads in the yard to take care of the slugs and snails.
Happy gardening in Hawaii. Gardens are where people grow.