Another bit about tomatoes, do put some time in on them when they're small and you'll love yourself later and so will the plants.
I plant in and put marigolds, either French or the special nematode chasing varieties (Golden Guardian or Nemagone) with the tomatoes. This is one companion planting that pays seriouis dividends. Two to four plants about 6" away from the tomato plant. (I plant inside the circle of the cages) This makes a big difference in the growth and production of the plants. Don't grow tomatoes without their marigolds! If you start tomato plants from seed, start the marigolds at the same time so they can go in the ground at the same time. Even in my RGGS (self watering pail system, or Rain Gutter Grow System) I will put 1-2 marigolds in each pail.
As the tomato plants grow and the training to stay in the cages start, I start removing bottom leaves and taking suckers. So that by the time a plant is 18" tall, it is clear to 6" from the soil to the first leaves. A 3-4 foot plant will be bare 12-18". I stop at about 18" on say a 5' tall or taller plant. This helps prevent a lot of disease issues, lets air circulate at the bottom of the plant, and otherwise makes later care of that plant easy. It helps to see the weeds easier to remove the competition.
I strongly suggest for anyone growing tomatoes, buy a copy of this book:
https://www.amazon.com/Giant-Tomatoes-Marvin-H-Meisner/dp/0975515314/ref=tmm_pap_swatch_0?_encoding=UTF8&qid=1505950218&sr=8-1 How to grow Giant Tomatoes. As he said, he retired and wanted to grow tomatoes, especially competition ones, and nothing out there was very organized, so he found out all he could, grew some, and wrote the book. It is for growing competition fruit, but. FIRST he tells you how to grow tomatoes. THEN he tells you, if you want to grow for greatness, how to do that. If you stop before the last part, you will have nice healthy tomato plants that will produce.
I can vouch that I use a lot of what is in that book, though I use things like DE,
compost tea, etc; and the companion planting marigolds. And I have grown for greatness. I've also started suckers and airlayer propagated tomato plants. Maybe your library has a copy or will get one for you. Good luck.
One more note, if it seems you are always hitting the hottest part of your growing season just as your plants are trying to set, it might solve problems to shift growing season by starting plants earlier or later to start setting before the hottest part of your season. I do two cold season, one hot season, and one long season that overlaps the others, here. It is a fight to get cauliflower and broccoli here as it has to come into maturity just before it heats up, then making sure the seedlings for fall are started early enough to finish out before coldframes won't work any more. Coldframes can be made from a ring of bales, an old window pane that will cover completely, and a couple of old blankets for cold nights/and or snowy days.