Nella, sounds like this little guy's gotten a new great home!
Yorkies can be picky eaters and they can also eat like a horse. It just depends on the dog, how he was brought up, etc.
My suggestion (and this works for me) is 2 meals a day, one morning one evening. You will over time learn how much to feed. I would also recommend putting down a good QUALITY dry food (not Ole Roy or Pedigree), something like Nutro's Natural Choice, or one of the GOOD foods. Keep that down for him to munch on during the day.
You can also offer him things like baby carrots, etc. Stay away from things like celery as the strings can create problems. My kids eat Brocc/Calif., green beans, baby carrots, etc. and they LOVE it and do well on them. Be sure to watch to make sure your little guy doesn't choke, but he should be fine.
And BTW (From your other post) 12 pounds is NOT unusual in a yorkie. When the breed was developed a mere 100 years ago, they were bred down from larger dogs, so occassionally a big one comes along. I have 18 yorkies in my house (most of which are rescues) and 4 of them are over 10 pounds. Just more to love. 
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Joan
Responsible Breeders spay/neuter Pet puppies.
Statistically, the average breeder remains in a breed for five years. The mark you leave on that breed, good or bad, is entirely up to YOU!