Maybe you could take a look at this website:
https://secure.balanceit.com/
I used the site & supplement when I home cooked for my pups. You can generate free recipes based on age/weight/activity level/allergies, etc. I would also recommened a supplement if you pup's diet consists of more than 1/3 of human food. Although the BalanceIt supplement adds a bit of a grainy texture, it smells flavorless. So it shouldn't be an issue for picky eaters. If your Westie has digestive issues, you could look into petdiets.com. You can get a nutritional consultation from Dr. Remillard online. I know that many YT members have had great experiences with petdiets.com & I've used them as well. Also, you could ask your vet about a probiotic to help with digestion. My Morkie takes FortiFlora.
To answer your question about types of foods that Yorkies can eat...yes, Yorkies can eat sardines & pink salmon. I would just make sure that if not fresh, they are packed in water vs. oil due to sodium content. My Yorkies love peas, carrots & apples. So I think yours should be okay. I give my pups frozen peas as treats & my puppy loves to chew on frozen green beans.
Congrats on your new pup & welcome to YT
