The sub panel is 100 ft away from the main 200 amp panel.There will NOT be any machinery (welders, table saws, compressor or any other motors except the washer and a secondary refrigerator). I'm thinking 4-#6 THHN wire enclosed in 1" armor cable in attic then buried in 1" pvc sch 40 and protected at daylight with 1" pvc sch 80. A 20 amp breaker dedicated to the washer (is this required to be GFI?), 8 outlets on a 20 amp circuit (GFI breaker), 20 amp to a box giving power to 4-CFL lights, a outdoor sensor light, low voltage landscape lights. I will be placing a BBQ area next to the garage in the future, so I will have to pull 1-2 outlets and 1-2 lights. Any problems?

You don't have a large load, but I would use #2-4 aluminum SER cable, and #2 AL XHHW where in conduit.

Washer would only need a GFI if within 6 feet of a sink.

Sch 40 is sunlight resistant, the Sch 80 is not needed, but is better. Would be better if entire run is Sch 80, as Sch 80 is considered as strong as steel rigid conduit.

Those are my suggestions.