Hi
I’m going to get terminology wrong here so apologies.
When I double click a glyph, it opens a window with that glyph.
I can add a line of text here, it takes about 20 glyphs in length, can I make this window wider to take more text
You can resize the window to fit the size of you screen. But you probably meant the edit view width. You can change it in Glyphs > Setting… > Appearance.