I made all three of the most common mistakes... The first was starting out too big (much larger than your plot - yours sounds like a nice size) & quickly getting so overwhelmed & disgusted that it was a couple years before I tried again. Second mistake was overwatering - I quickly learned to stick my finger deep into the soil & if it's completely dry it's time to water. Third mistake was not fertilizing. That's as bad as overfertilizing. It took a few years of trial & error, but I finally figured out that an inch of composted cow manure on each new crop is all I need for most things. I use fish emulsion & liquid seaweed if I need something extra, & am trying turkey compost on the heavy nitrogen feeders this year. One more piece of advice for you - if you ask five gardeners the same question you'll get six opinions, so try not to get overwhelmed by it all. Good luck! And don't ever forget that this is supposed to be fun. :)

Rent a Rototiller or buy one (link URL below). It will rip out all roots, rocks and weeds. You can then till in some compost, add organic nutrients like Rock Phosphate, green sand, Blood Meal, Bone meal and you have a great start. If you have very bad soil, add in some vermiculite (expensive) but it will greatly improve your soil quality. Alternatively you can use raised beds but that drives the cost up as you have to buy soil as well as the hardware for setting up the raised beds. Here is a link that might be useful: Light weight but powerful tiller

Helianthus I believe.

How is it going? How soon after pulling out the weeds did you post? It might take a few days for pollinators to discover the flowers after you clear the space out. Also, you can hand-pollinate squashes -- often with better results than with bees. And I would do the other plants, too, in case it works on them ;).