The hoodie has really progressed. Excellant.
THis is a video
for slip the first stitch purlwise that shows you the chained edge that you get when you do so.
There's not really a best way to do the increase. It's more a matter of keeping track of your stitch number and your personal preference for increasing. In you case, since you're increasing in the last stitch, keeping track of stitch number won't be a problem. So it depends on the look that you want. Knit front and back, KFB, will work but my favorite is knit left loop, KLL, or knit right loop, KRL since they won't leave a little bar across the front. All these are demonstrated on the Increases page under Free Videos at the top of this page and all of them (and others) will work for you.
These are both great questions, btw.