I did a print-inspired quilt a couple years back, kind of a two-color poster look, and the thing that made it work was picking one texture and committing to it hard. If I were you I'd go with the grid over the waves. Halftone is what people's eyes actually read as printed, wavy lines read more like water or woodgrain. Keep the grid lines about half an inch apart, straight stitch with a walking foot, and don't stress about perfect spacing. Slight wobble actually helps here because real print registration is never perfect either. If you want to push the halftone idea further, you could do a loose grid of small circles or little X's in the background instead of full lines, but that's a lot of marking and stop-start work for a wall hanging, so I'd only bother if you enjoy that kind of slow stitching.
On thread, I'd resist matching each section. Matchy thread flattens everything out and kills the offset-ink feel. The whole riso vibe comes from layers that don't quite line up, so let the threads do that too. Orange thread on the pink areas, and something like a warm coral or even the blush on the orange star, would give you that misregistered edge everywhere you stitch. The trick is to quilt from the back and just barely let the bobbin thread peek thru on the front, or run your lines right along the seam lines so the color shift happens exactly where the block changes. That seam-line quilting is what made my version look intentional instead of accidental.
For the border, I'd actually vote orange, but a slightly deeper orange than the star so it frames it like a second ink pass. Pink border would blend into the background and the whole thing might float away. Stitch the border in the same grid continuing right off the edge of the blocks, so it feels like the print runs past the margin.
One last thing, go slightly lighter on the batting if you can. Low-loft keeps everything flat and crisp, which is exactly what you want for that flat printed look. Puffy batting would make it read cozy instead of graphic.