Need help with a inventory sales prediciting spreadsheet

Hi all,

I'm trying to make a excel program for work. Basically what I want to be able to do is; enter promotional history for an item, specifically the price of the sale item, units sold, temperature during the sale, total sales and number of like items also on promotion. Then I want to run a multiple regression to forecast the sales for the item the next time it goes on promotion. I'd also like to have some charts to track sales of the item.

I've been able to do this to some degree (the bare basics) however it's not very easy to read or maintain. I really need something that's able to handle 200-400 products, along with at least 12 different historical promotions. What I'd really like to do is something similar to this http://youtu.be/vur4yH3Aoec with the drop down boxes where I can pick the data i.e product, price, temp, forecasted total sales and number of like items on promotion. Then click forecast and it will run the regression for the imputed variables and give me the forecast.

I would also like an area where I can easily input the recent promotional history, so the forecast can stay up to date.

Now what I want to know is what I need to learn to be able to make this? What excel functions I need to know to be able to make this. Because i really am lost as to where to begin my learning. I'm reading through a lot of the threads on here along with watching youtube demos but i just want my efforts to be more streamlined and to the point.

Thanks in advance for any help people and can provide

Regards.