Did you say you bought the pattern already? If so, you can CAREFULLY pin it together and try it on. It will be only one-sided unless you make a second tissue front side to make it whole. But you can see if if is even close to the right size in that way. Many women who sew make a muslin up before cutting into the fashion fabric. That way you know if it needs altering. You don't have to put the facings onto the mock up. Just see if it is the right sleeve length and width and that it has enough ease in the back area to feel good wearing it. A biggy with me is that the bust seam line hits in the right place.
I love the one you chose. Very runway chic! Yet a classic.