liz- i'd move this post over to the discussions board if i were you; it's not really and exchange and you'll get a lot more responses.

that said, your collards, cabbage & kale will go all winter unless it's more cold than normal (i'd maybe consider covering if it's gonna dip below 15). you could grow them under reemay/row cover, too, which will help the fluctuating temps & moisture levels some. also cuts way down on cabbage worms. i couldn't believe how much it helped my lettuce last yr.

i've always wondered about starting things when it's so hot, too. i don't know if the commercial ones start them in cool houses, or what. mine are always far behind, but they do fine in winter. they will just mature later, that's all. you could always buy a few commercial 6 packs and plant them so you have a staggered crop.

i've grown tomatoes pretty tightly before, and the problems i saw were if a disease hits, it spreads fast and you're less likely to notice it since it's so crowded. ditto for bugs, though i didn't have any issues with that that time. about the only bug issue i ever have with tomatoes is hornworms, and kids are especially good at spotting them once trained. disease resistant cultivars could help with those issues a lot, but it's hard to find really resistant varieties that taste wonderful. on the plus side, there's very few weeds because they are shaded crowded out. so, pick your poison, so to speak. i think there's a nice middle ground, the trick is in finding it ofr your situ. it depends too on whether you are talking about indeterminates or determinates, and how you support the vines. the more air and light you can get to each plant, the better for disease.and the better they'll grow, as they'll compete for sun & shade each other some.
good luck! tam