You can cast on the front and back stitches, knit it in the round to the underarms which you bind off and work the front and back flat separately, shaping the armholes just the same as in the pattern. Then do a 3 needle BO for the shoulder seams. For the sleeves you can do them a couple ways - knit in the round to the underarm, BO stitches and work the cap flat just as written and sew into the armhole. Or you can pick up stitches around the armhole, shape the caps with short row shaping and knit down to the wrist with decreases.
Since this is your first sweater, I think one worked top down will be easier, you won't have to convert anything. Here's a couple of pattern generators where you put in the gauge you have and finished measurement you need and it gives you a pattern: