Why not start simple and use a radio button option to select 1)start/end date or 2)recurring payment/income timeframe.
start/end date options are obvious. Recurring payment/income shows a list of recurring payments that are in play(I assume you can show just those). User selects one of those to chart within. Once they have selected which one, they are given a drop list of cycle dates to use as the start date. Then you add a field for number of cycles to show.
Hi Eric 8)