Work top down. Start with hanging decor along the schach line — garlands, greenery, spinners — because that sets the frame everything else sits inside. Then the walls: a large tapestry or artwork on the main wall, posters and sculptures around it. Then the table. Doing it in that order saves rehanging.
The frame, always. Nothing should be fixed to or hung from the schach. Command hooks, clips and cable ties on the frame rails will hold anything on this site, and frame-mounted decorations survive wind far better than anything pinned to a wall panel.
Give them the walls at their own height and let the results be imperfect — that is the tradition, and it is more memorable than a perfectly styled sukkah. Craft projects, paper chains and their own artwork at child height, with the breakable and expensive pieces hung high out of reach.
Vinyl artwork, laminated posters, artificial greenery and metal sculptures all handle it. Fabric tapestries and anything paper should go on sheltered walls or come down when a storm is coming. Whatever gets wet, dry it fully before it goes into storage.