1. Thinking that using foundation or makeup with SPF will be enough to protect your skin from sun damage or sunburn.
Suncreen should be used daily even if you're wearing a makeup with SPF.
SPF factored is tested by measure how much protection is in each 2mg of product over a cm surface area of skin. In order to use that much protect, you would need a lot of powder! Approximately 7 times the normal amount of foundation and 14 times the normal amount of powder to get the Sun Protection Factor or SPF on the label of the cosmetics with SPF.
Foundation offers a bit better protection but the recommendation is at least 1/4 to 1/3 a teaspoon of sunscreen for the face in order to get the full sun protection. Most people probably use less foundation than that, so don't forget that sunscreen before heading out!
2. Does Oily Skin Needs to be Moisturized?
Yes. There is a difference between oiliness and hydration. The goal is to make the skin balanced and clean, not to dry it out.
Oil production in the skin is a natural and vital part for it's maintenance. If the skin is dried too much, it can becomes irritated and scaly while remaining oily.
The irritation and over-drying often contributes to acne as the oil becomes trapped beneath the dry, flaky layer and becomes a source of inflammation.