In John Palmers How to brew his amber ale recipe has 900g of 2 Different sorts of Cyrstal 60L and 90L. and his brews are 19L recipes
I would go for at absolute minimum of 500g for an amber ale.
like palmer does, instead of using just one type , you can use two different shades, it will contribute a greater depth and character to your brew than just one. you could even use three. light med and dark.
im drinking a one now that was a cascade pale ale kit with 1kg malt and 250g 30l and 250 60l Crystal with amarillo that turned out quite nice.
Ayways knock yourself out and sounds great. Peace
