1. No, not true. A high-fiber, fortified food should make up approximately 90% of your hamster's diet. A complete fortified food such as Oxbow’s Essentials Hamster and Gerbil Food would be the best option. You don't want a diet that contains a lot of seeds.
https://www.petco.com/shop/en/petcostore/product/oxbow-essentials-hamster-and-gerbil-food Here are some things you can try to offer in small amounts as a treat:
Asparagus
Baked or Steamed Chicken, Turkey or Cod Fish (Skin and bones removed.)
Bananas
Boiled or Scrambled Eggs
Blackberries
Blueberries
Cantaloupe
Cauliflower
Cooked Brown Rice (plain)
Cooked Whole Grain Pasta
Flax Seed
Lentils
Mango
Melon
Mild Cheeses
Nutritional Yeast
Oatmeal
Plain Tofu
Raspberries
Romaine Lettuce
Seedless Apples
Seedless Grapes
Squash
Strawberries
Sweet Potatoes
Unsalted Popcorn (no butter)
Unsalted Pumpkin Seeds
Unsalted Soybeans
Fruit and whole grains can upset the GI tract if offered in too high levels. As a rule of thumb, only 5-10 percent of the diet should be these foods.
2. No, on any citrus fruits.