Firstly, thank you for the compliments and the feedback.
And yes I totally agree with you both that if I were to take it further, then I would make custom maps to the rhythm and obviously faster songs would be harder etc, etc.
For combos, initially it was for every box hit but the score was getting way too high so I made the quality of the timing of hit affect the percentage that the combo goes up by. I suppose I could have worked around it instead but it was good to hear your opinion on it thanks.