My little guy was neutered at 5.5 months. As an adult, he's just under 5 pounds. I recommend kennel cough and rabies shots. Be aware, at that size, you want to space out shots. My little guy aches after some of his shots, and I give him painkillers for a day, possibly two.
You will want your own pill cutter! The heartworm medication, while right for his body weight, doesn't fit in his mouth. I have to cut the pill into four pieces for him. Fortunately, he thinks it is a treat and chomps them down easily each month.
There are a limited number of harnesses that will work for yorkies this small. I even had to do a little adjustment on the one I finally did find to make it just right.
I'm sure you already know that you need to keep a doggie first aid kit handy. I also make sure that I keep a few cans of chicken breast, packed in water with no salt added, so I can whip up chicken and rice without messing with trying to quickly cook chicken. I also freeze little bone shaped cubes of beef broth, to entice my picky guy to consume a little more water when I think he's been out chasing squirrels for too long. (He's CAUGHT squirrels, twice!) That way, I don't throw out most of the broth before he has a chance to enjoy it.
I find my guy looks best in athletic wear and doesn't get embarrassed at looking too floofy. He has several football jerseys, a few baseball shirts and two denim jackets. One has a polarfleece lining and the other one has both polarfleece and thermolam lining for our very cold Wisconsin winters. He will not tolerate socks or boots, I've tried...
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Sleepypod carriers. They've been crash tested and are wonderful for traveling with your dog.