There is no such thing as a Microlight rating under JAR. If you hold a SEP Class rating then you can fly any single engined piston aeroplane of any weight that does not have a type rating. The microlight has a single engine with pistons so you can fly it on your SEP Class rating.
This was clarified in AIC 3/2004 White 92 after much confusion over non existant ratings.
Hours flown on microlight aeroplanes do not count towards SEP revalidation or towards the CPL.
As with any aeroplane that is substantially different, you should undergo familiarisation training before flying it solo, this is particularly important with weight shift microlight aeroplanes.