I need to create monthly revenue projections for each customer (custom fields? maybe a custom record?). Then on the customer dashboard I will need to show projection vs actual sales by month as well as a ytd running total, ideally. I assume I will have to script this, but I don't know where to start. Will a custom list portlet do this? Any ideas?

Are they using Opps or Estimates?

'They' aren't doing anything. They're just going to give me a list of numbers for each customer for each month. I looked at creating custom budgets for customers, imported a few, but I'm not sure how to use that.

So one way would be to create a custom record sublist on the customer record (parent) with period, period start date, amount, currency, etc. and then to create the relevant analytics from there but you would have to make sure you're able to pull actual revenue per customer in the analytics (I did something similar for another client)

I did create a sublist on the customer page - but it's simplistic, just 'Month X' with an amount in each field. Actual dates may be helpful. I was hoping to use analytics for this, but the analytics portlet is not available on customer dashboards it seems.

Right - but even if it was available on the customer dashboard would you want to go through all the customer dashboard to be able to see a revenue projection? I assume that 1 graph for aggregate revenue projection / period and 1 graph for revenue projection / period / customer would give them a good start

No, they specifically want it on every customer dashboard. This is for the sales reps to use and they frequently visit their customer dashboards for other info. Sorry, I was not specific about that.