Can't find any qtcharts on freenode. Anyway :

Data :
- what data can you handle : integer / double values, labels, min/max indicators, complex values, quaternions, ...
- do you use a model-view approach or not ?
- will you have only 1 data series, or more (multiple lines in your graph)

Display :
- are you going to make different display classes for the qpainter and qgraphicsview ? Will be difficult to make sure they look the same. QGraphicsview is not required for just showing graphs, but is sure is handy for interactive graphs (selecting data points, pie slices, ...)
- are you going to stick to line charts and pie charts ? or also bar graphs, coloured maps, ...

Classes :
- I would make a 'QtCharts' object that can hold any kind of data, for 1 or more data 'lines', and also additional data like labels, min/max values, .... This object could then be painted by the painter classes, be it either pie or line.

Regards,
Marc