trying to teach myself financial modeling. a few questions

I havent really seen examples of this anywhere on the internet, which im a bit suprised about as i thought financial modeling would have alot more discussion online.

Anyways, a few things i cant figure out how to do:

  1. A project is designed to re position a product in the market place, the goal of the project is to increase its marketshare. How do I forecast sales/projected market share growth when the previous sales data was not solid due to poor product positioning?

  2. As a result of the repositioning, customers are expected to buy more of product line A. Canibilizing sales from the other product lines. How do I best reflect this change in product mix in the sales? Do I just make it an assumption and multply the sales of all product lines by a guestimate factor on how the product mix will change?

  3. inventory analysis: If i was doing a project for a specific customer group, how do i reflect the inventory section? For example, if my company has 50 million units of inventory. But this project was designed to only reach 5% of our customer base, it seems like it wouldnt be pertinent to include our massive inventory stores in the inventory section. How would i reflect this? Or should i include the companies inventory as a whole, but only have the purchasing as go up 5% ?

thanks in advance if anyone can give some quick feed back on that