The short answer is 'it depends'.
In general I think the less time you have to train, the more structured it should be.
'Riding for fun' is fun, but so is winning. Pick which is more fun for you.
Anyway, given you've just upgraded (congrats), I suggest getting a feel for cat 1/2 racing. Many find that it's like learning to race all over again - some give up, some keep going. Be patient.