Hey there,
I'm not sure what a chiweenie is? sound's like somebody's dachshund got into the chihuahua pen? LOL
I second what fw said. SOCIALIZE the heck out of that puppy. Take him everywhere. Make him walk on the ground. Remember he has (almost) all the same genes as a timberwolf. The shaking usually has nothing to do with being cold in chis. The more you socialize him, the better his quality of life will be. Treat him like a real dog. This means getting him in to puppy class ASAP. Even if you have trained dogs before. Rememember, even the best professional dog trainers in the world take their new puppies to puppy class. It is virtually impossible to reproduce at home the experiences your pup gets from a good puppy class.
Unfortunately, leaving his litter at 6 wks will put him at a disadvantage, but you can make up for it somewhat by getting him around puppies as frequently as possible... controlled, positive experiences. Nothing can replace the 24/7 contact with littermates and mom, but we can make up for a lot. As long as he is playing with VACCINATED, HEALTHY dogs and pups, he should be safe. But definitely steer clear of dogs whose vaccine history is unknown.
I usually tell my clients to commit to giving their pups at least 1 new experience every day until they are 16 wks old. Then 4/wk until they are 6 months. Then weekly for the rest of their dogs life. This means taking your dog out of the house, meeting a new person, walking on a new surface, encountering new animals, etc. It's not that hard if you put your mind to it, and truly makes a remarkable difference in your dog's quality of life.