For exterior: Should I wrap the vertical exterior plastic pipe (3/4 inch ) with the electric tape then install fiberglass tubular insulation over it to keep dirt off the tape?

Do not wrap self regulating cable around the pipe in a coiled or spiral fashion, and do not use electric tape to attach it. WarmlyYours recommends attaching the cable in a straight run and to use aluminum or fiberglass tape, pipe straps, or plastic zip ties to attach the cable. Then cover the assembly with fire-resistant insulation and assure it is waterproof. Place electrical heating cable WARNING labels every 10‘, and where the label will be clearly visible.