You can always sign up to be member and start paying to the A-kasse.
You can also free chosse between be full-time or part-time member, BUT the the most important for you
is how much you can get in unemployment benefits if you get umployed.
To get benefits as fulltime member you must have had at least 1.924 hours of work during the last 3 years.
But be aware although you are entitled to benefits as a fulltime member, it dosn't mean that you always can get the max. amount payed.
It depends on how much you have worked the last 3 months up til you get unemployed.
As a fulltime member there must be registered at least 320 hours work in the calculating-period.