Yes, that's extremely common and expected. Generally you charge 3x the rate you pay.

If you are pricing hourly, yes. You will be able to better map value and price to your customers' needs.

In my experience with designers for more than a decade you've to fix the price based on average cost of all your resources If you do it you will not be able to check the costs involving multiple resources. If you wanted to bring transparent pricing model educating your clients are challenging. Alternatively if you have enough experience to understand the resource needs with less than 2% deviation then work on different costs involved and come with a standard pricing.