I reckon your best bet is the Open category for the first time. See how you get on then enter Sport in your second event, depending on how you go. Believe me, when race fever takes over, it seriously bursts the lungs, even in the Open category!
Well finally got round to entering the Aberfoyle race. Is it all fairly straight forward? Turn up...sign in sorta thing?
I am interested, is there a link to get event dates?