What a precious little doll. I think everyone is giving you great advice. Most important is to treat him like a dog, not a baby. I know it will be hard, since he is such an adorable baby, but Chi's are smart little guys with a lot of heart and you don't want to end up with a dog that no one wants to be around.
He needs a crate, his own little condo. Never ever let him sleep with you, especially now, as tiny as he is now. Humans could roll over on him and that would be bad, or he could jump or fall off the bed, and that would also be bad.
My husband wanted a tiny Yorkie for awhile and we did some research and decided that they were not right for us. I do remember reading that they need to be fed tiny amounts and often. Something about hypoglycemia, I think. Have Nutracal on hand just in case. Or whatever your vet recommends. Oh, we ended up rescuing a 20 pound Yorkie, or Silkie, we are not sure. The breeder was a hoarder and they were all taken away, and she bred and sold both Yorkies and Silkies. . So she could be a mix of the two or a large Yorkie.
We used to raise German Shepherds and from what I hear you can train a Chi the same as a GSD. Start early and have lots of patience. My pups could sit and stay and were pretty much potty trained when they were sold at 8-12 weeks. I see no reason why your little guy could not be just as smart.