I would suggest that you do not need to create a new Opportunity each month. It may be simpler to add custom fields to your Line Items to help you classify each of the Products. For example, you could have a new column which determines the Payment Type, either 'Single Charge' or 'Ongoing Monthly Payments'. You may also want a column which store the 'Monthly Charge' for those Line Items that are recurring.

The when you are reporting on the Opportunities to determine the commission for your Sales Team, you can drill through from the Opportunity to the Line Items to fetch the data from these custom fields. You can create calculated columns that determine the amount should be included for each Line Item, e.g. if the 'Payment Type' is 'Single Charge' then output the full amount from the line, if the 'Payment Type' is 'Ongoing Monthly Payment' then output 12 times the 'Monthly Charge', and from there calculate the commission. If you then create a summary view which groups by Opportunity Reference, it will add up the calculated values from each line into the Total Commission for that Opportunity, and you can group by the Assigned To of the Opportunity to get the Total Commission for each Sales Team Member.

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