I have been playing with name banners for my family for years. Thought I would pattern some common phrases. I used DK and the letters are 14cm, but, if you use 4Ply, hey are perfect for hanging, Chunky they are 30cm
You need 4mm double pointed needles just because they are easier to knit small items with. Long pins are fine too & everything is knit flat. You need to know how to do short row shaping.