#1 - Welcome to the Forum!

#3 - they ought be universal, but the size is 1.5" - maybe you made a typo?

#4 - you should match the new skimmer to the old one, the screw holes vary, even for the same sized skimmer. If you can, take the existing faceplate to the store when buying a new skimmer. (this isn't 'fool proof' but is a good start - the best way would be to find out the model number of the existing skimmer and order one that matches it)