Stretching mock cable

Thank you for the link to blocking tips. Hope to get your input on specific questions I’m wondering about. I’m currently knitting a cardi, will be 5 pcs to seam together when done. The yarn is a "super bulky ", 82% acrylic, 10% wool, 8% rayon. “Machine wash & dry”. So, it looks like washing/soaking is recommended BEFORE seaming right? Should I handwash or machine wash before blocking? Since it’s mostly synthetic fiber should I even bother blocking? The pattern is Moss stitch with hem and cuffs of 1x1 ribbing.
I’m not finished but I look forward to your advice😉