Why do plates look blank in blueprints?

Display plates use the rendering API. The advantage of this over the picture variations method is a very memory-friendly entity prototype that is independent of any other mod's sprites. The disadvantage is that the plates look blank in blueprints and when they are ghosts, but the settings are restored when the plates are actually built.

The icons are fuzzy?

Low resolution icons (32x32) look like crap on a large display plate when you zoom in to the game world. There's nothing I can do about that. 64x64 or 128x128 icons look better. The vanilla Factorio game is gradually being updated with 64x64 icons and the full set is expected for the 1.0 release, latest. Your favoured mods may provide decent icons as well.