Lots of questions here, I won't answer them all but 1) cukes and squash are somewhat hardier than tomatoes. I typically put them out a week earlier than toms. They will take 45F without flinching while toms prefer 50F or more. 2) for SVB, aluminum foil or spraying the base of the plant are possible strategies. There should be only one generation so if you spray consistently (the base only) you may get them. Around here, typical times for SVB are June 25 to July 5. 3) cucumber beetles are earlier than that, and they will transmit diseases to the plants early on. I suggest that you spray the whole plant well until first bloom. From that point on, you will have to be happy with what you get. 4) showering the plants with compost tea helps with leaf disease.

If a brown color is evident in the slits then chances are you have the SVB. In this case, you may want to try using a skewer to probe in the slit to find & root out the worm. Do this before the plant wilts as noted in the above post.

Here's an up close and personal look at the enemy. Funny story, I'd never heard of SVB. Every year my dad's squash would get "stem rot" and die back. Frustrated him to no end. The first year I started any gardening of my own, I was growing some veggies, including some crookneck yellow squash in containers, since my dad didn't have room in the garden to give me any space. One day I was at the local nature center and saw this "cool" red and black moth feeding on rattlesnake master. I'd seen them in my yard a few times. Took a series of macro shots (attached is one of them). Went home and googled "red and black moth IL" in image search, spotted the same moth, clicked image-- and at the top of the page in bold letters was the common name: SQUASH VINE BORER At that moment it occured to me my squash were looking a little sickly. It didn't take long to figure that they'd been killing my dads squash every year, which he thought was the stem rot. And thus my (still mostly losing) battle with these things began. Wiped out my crooknecks that year. I managed to keep my squash alive last year by injecting with BT and heaping dirt on the vines to get some new roots, but ultimately production went down to nearly zero on the two survivors.

Didn't know what she looked like, just been checking for eggs. It pays to spend time in the garden, checking things out. No, gardening in never boring!!!!