What are you using to estimate the 10K sales number? Do you have a history of sales with this audience you can use to estimate conversion rate? You can't really estimate beforehand how the conversion rate will change from $0.99 to $5. You might make 9,999 sales at $5 or you might make 100 sales. How customers respond to price depends on the product and how they are paying for it (in-app vs. entering a credit card on a site), as well as the nature of the customer. Is your product one amongst many competitors, like an app in an app store? Or is it more unique like an eBook relevant to your niche audience? Customers in the app store will be much more sensitive to price than your engaged users, especially if what you're selling is unique. Finally, beware of underpricing. You can always put something on sale but it's very hard to raise your price.

Having different subscription plans makes sense in two scenarios. First, if each module is itself a service that a customer might subscribe to on it's own then it makes sense. Second, if you are charging based on metered usage like AWS. In the first scenario where each module is it's own service you could construct subscription plans for each and provide discounts to incentivize customers to use more than one module. If these are just add-ons to a core service then I don't think this is a good idea. It just makes the decision more complicated for your customer.