Hi & welcome to YT! I bathe my 3 on an as-needed basis, which is usually bi-weekly in the summer, and maybe every 2 1/2 weeks in the colder months. There are alot of shampoos/conditioners that I like, with a few of my favorites being:
Yorkie Splash and Shine,
Nootie, Petsilk, and the Paul Mitchell products. The first two are offered by YT vendors, I included their links.
If you have friend who can purchase from a beauty supply, the Paul Mitchell products can be picked up very cheaply!
I feed my pups Wellness Core, but the light variety, and every now and then mix in some Merrick Before Grain Chicken formula.
The only advice I have about food is this: Baxter developed kidney stones, and has to have them removed. My vet recommends feeding dry kibble only, as this will make the pup drink more water. There is much moisture in canned food, which causes them to drink less. Before this happened, I fed them about 1/2 canned & 1/2 kibble. It took a little while for them to adjust to just dry, but they are fine now!