In regards to knowing when they are large enough for harvest I was told by a very wise farmer, " Just reach you hand in there, between the leaves and if it feel like a 42 Double D...it's ready."
I prefer eating cauliflower over broccoli that's for sure. My favorite way is just steamed. Roasting is also an A+ choice. On my To Do List for tomorrow is to can those little snow white (or green, purple, or orange...in love with colored cauliflower!) florets.
It's pretty trendy to make cauliflower into "rice" or mash it. Here's some links to some great recipes so you can give it a try:
Cauliflower Fried Rice (with Sriracha)
Cauliflower Fried Rice
Cauliflower Mashed Potatoes
Garlic Mashed Potatoes