From a quick bit of internet research:
Flowers were traditionally carried by brides as a symbol - different flowers meant different things; ivy for everlasting love, orange blossoms for happiness and fulfillment, and sometimes even herbs and spices to frighten away evil spirits.
There are no known instances of a child being "thrown out" when his bathwater was disposed of. This saying means more along the lines of not throwing away something important when getting rid of rubbish.
Dogs living in roofs? That's a little far fetched.
Canopies over the bed may well have been used to protect sleepers from falling items, however it would likely have only applied to the wealthy.
"Dirt poor" is an American expression, not English. "Dirt" was never directly translated to "Earth" in English, it was used to refer to excrement ("Drit").
While the etymology of threshold has not been completely nailed down, the thresh portion is understood to derive from an ancient Germanic root meaning to "trample" or "tread".
Bring home the bacon may well be correct to some extent, but not that they would hang it up! It would appear that "chew the fat" came from the American term "chew the rag" which initially meant to grumble or complain, and the essence of the term has weakened over time to just mean idle chat.
Tomatoes have a low acidic content compared to any citrus fruit, so why tomatoes and not apples?
"Upper crust" was originally used to refer to the hat or head, and then later to the Earth's surface. It wasn't until the 1800's that it was linked to aristocracy, and the connection probably arose from the link to "top" (as in hat/head).
That was as far as I got before I decided I had to get back to work!