There's not much to say, because the finishing touches were simple, albeit VERY time consuming. The painting took hours and was difficult on the linen. The warp stayed. Next time, I'm going to seal the whole shield in linseed oil on BOTH sides simultaneously and hang it vertically to dry, hopefully preventing any warp. We'll then see if I decide to use linen again; that and the glue add ample weight, though they increase integrity. Plain wood would take the paint better, I think.
My penultimate step was to rim the edge with a strip of soaked rawhide, with copper tacks on both sides of the shield about an inch apart each. This task also took quite a while, but provided exactly the aesthetic I love, the historical accuracy, and also the integrity it was intended for: the rawhide hardens as it dries, resulting in a durable edge that also keeps the shield in shape and the boards tight together, explaining why the Vikings simply butted the boards together with some glue other than interlocking them with grooves somehow, which their prolific woodcraft and detailed carving work surely shows they had the skill for.
I had to decide between a wooden and an iron handgrip. I opted for iron after consulting Bill Short, expert on Viking combat who works extensively at Higgins Armory Museum in Worcester, MA. He told me they both were prevalent, but the iron provides greater strength at roughly the same weight, and more importantly, the grip of the hand would be closer to the spatial center of the shield rather than off to the side, providing greater ease of pivot and less fatigue on the hand and arm due to ungainly weight distribution.
As my eye for volume and length distribution in blacksmithing still isn't great, I cut this shape out on the plasma cutter to ensure it's symmetry. However, I still put it in the forge for a while and covered it in scale and light hammer blows to get the right looks! I drilled holes in the grip and the shield, both for the grip and the boss. I attached them all with clenched nails per period. It worked well, but once again, I resolve to use washers on the back side on my next shield to prevent cracking. A partial success in functionality and a total victory in learning!