I think that you can do it. I have set the Global Reward Point Ratio to 5.00 with Catalog > Reward Points. This gives 5 points for every currency unit ($, €, £ or whatever your base currency is) spent, which is redeemed for 0.01 per point. That covers your question about the formula.

If you go to Configuration > Reward Points > Adjust Reward Points for Sales/Specials you can set it to 0 or 1 depending on what you want to do. Each of the options is explained there.

Although I have not played with it, I see that you can define a different Reward Point Ratio for a product. Go to Catalog > Reward Points where you will see the Global Ratio of 5.0000 in the box on the top right of the screen. Then, select a category and a product. You will find another box titled "Set Product Reward Point ratio:" where you can enter a different ratio for the individual product. In your case, if you don't want some products to earn points, enter 0.0000 in the box.

As I said, I have not tried it but this should be the purpose of setting a ratio on a product basis. You may for example want items of sale to get 2 rather than 5 points for every dollar spent, or you may want some other products advertised as earning 20 points per dollar. I can't see any way to do it automatically, so I assume that this should be done manually for each product differentiating from the global setting.

If you try and it works this way, you may want to post your experience here for other users to learn and benefit. Good luck!