The musk you would be adding is dependent on the scent you wish to achieve. You should see fragrant and essential oils as interchangeable, rather than two separate things.
Most FOs and EOs mix well. Rather than shaking the final product, warm the bottle between your hands and just gently roll it on a table or tipping it up-side-down. With all perfumes, definitely leave it in a cool, shaded area for a week for all the initial scents to blend before tweaking it again.