Wouldn't really worry about the chain rattle. Aslong as it disappears when warm thats all that matters. When the engine is warm the cam chain tensioner tightens the chain so there's nothing to worry about. I just normally use 10 or 15w 40
Alloys, there's a lot that fir the Micra. Alloys from a Corsa are a popular choice.
Aslong as the PCD is 4x100 and offset around the 38 mark.