Q: When using a bundle with Walmart will sku grid know to calculate the price of all items and use the formula to check if together they're more than 35$?
A: For Bundled items, yes, you can bundle multiple different URLs from the same supplier; however, you cannot do a "multi-pack" -- which would be 2 or more of the same supplier URL.
Yes, your bundled item will take on whatever formula you have assigned to it -- whether default or override formula, whichever applies.
Q: What about the Walmart price over $35 will sku grid know it's free shipping by the formula?
A: If your bundle is above $35, you would set Combine Shipping to NO. That way Sku Grid would exclude the shipping in the calculations.
OR
You can leave it as is and leave Combine Shipping = Yes. But then you'd need to create an override formula that has include supplier shipping in calculations = NO. It's not going to know not to include shipping if the bundle is over $35. You would have to tell it to do so either way.
A: You can add as many items as you want into a bundle.