Dog sweater

I am doing a Bernat dog coat I did the five row in knit do I start with knit or purl

Welcome to the forum!
Is it this pattern?

If it’s a similar idea, knit 5 rows in garter and then switch to stockinette, you could start the stockinette with either a knit or a purl. I tend to start with a knit stitch to keep increases on the knit rows but since this coat increases on every row, that won’t matter.