Upgraded iPhone 5 from iOS 6 to iOS 8 (MBP Mavericks)

I inadvertently upgraded iTunes 11 to iTunes 12 last week, and found that on my 2012 MacBook Pro I could no longer sync my iPhone 5 running iOS 6. So, I upgraded my iPhone 5 to iOS 8. My problems have now doubled:

(1) iTunes 12 does not see my iPhone 5, and therefore will not sync. The phone is plugged into the laptop.

(2) On the iPhone 5, even though I entered the correct password to my Gmail account in SETTINGS on the iPhone, the phone continues to insist that I enter my Gmail password in SETTINGS. I go to SETTINGS, enter the Gmail account name, click next, and I get a spinning wheel that goes nowhere.

So, how do I sync my iPhone 5 running iOS 8 to my Mavericks MBP running iTunes 12, and

how do I get my iPhone to accept and remember my Gmail password? The password is correct. I've tested it on my MBP and on my 3rd generation iPod Touch.