On the health front... My most recent arena run had me win 3 different games after dropping to <4 health. 1 of which I got smacked down to 1 health right after finally wrestling control of the board, when my opponent had finally run out of useful cards. I managed to get a giant wall of minions in play immediately afterwards, complete with taunt, but it still ended up being 4 turns of hoping he doesn't top-deck any direct damage. The game is absurdly full of those low-health situations. As people have said, the only health that matters is the difference between 1 and 0. And the difference between 12 and 13. And the difference between 30 and 29. Also, every bit of health between 10 and 21. But those later ones are for odd situations. There was that good old warrior deck back in the day where if you lowered the warrior's health below 15 and didn't immediately kill him you were dead.
As for the priest buffing thing: If he buffed a creature that high that couldn't immediately attack-- he was desperate and you had 'won' anyways. I've played a decent deal with those priest decks and know that the whole trick is figuring out a way to start your turn with a 7+ health minion so you can immediately pop the combo and win. The 2/7 turtle is a good card to try with, but the 2/7 berserker guy works better since people generally won't do any damage to him unless they can outright kill it. Oh-- and that priest deck can run a ton of removal and very few creatures because of how its buffing works. Something like 10 cards removal, 14 cards creature, 6 cards buff. (The +2 health, the double health, and the health->attack)
Anyways, I don't even play constructed anymore. It is far too gamed up with all those perfect constructed decks, detailed win odds figured out and whatnot. I'd find it much more fun to program an AI to automatically play constructed, since there is no thought or creativity left to it. I do, however, play a bunch of Arena. All those lovely unique decks, the logic behind creating them.... its so much fun. And supposedly I got good at it since I've managed 2 separate 12 win runs and I bring in enough gold playing arena to continue playing arena. I feel so sorry for the pigeon hole victims of mine. But it really gives a different feel due to the uniqueness of the decks. And it always feels good to beat someone after they've played their 4th Holy Nova.