Which glue could I use to fix the front panel?

You shouldn't need to use glue on your iPad repair. There should be adhesive that comes with the repair kit that you buy.

Here's a picture of the adhesive map for the iPad 4

Here's another picture without the map.

If the adhesive doesn't hold the screen down all the way – sometimes this happens if the adhesive is poor quality – you will want to use super gel. You can find it on Amazon here