In simple terms, the main difference is that under the Regular License, your end product (incorporating the item you've licensed) is distributed for free, whereas under the Extended License your end product may be sold. If you're a freelancer, you are allowed to create an end product for a client using the Regular License and charge them for your services.
No, our Regular License is for a free end product (whether or not the item is used in the end product in an editorial way). And our Extended License is for an end product that's sold (whether or not the item is used in the end product in an editorial way). If you want to use an item in an editorial way in your end product, choose the Regular License if your end product is distributed for free, and choose the Extended License if your end product is sold to the end customer.
If the end users need to pay to see the end product, you need an Extended License. There can be more than one end user as long as there is only one end product.
If the item is part of a product for sale, you need the Extended License.
As long as all end users can freely access the end product, the Regular License is fine. There can be more than one end-user (the person who uses the end product, such as the end consumer) as long as there is only one, unique end product.