To remove the “Add to cart” button on ALL products in your store, you can activate the option “Hide “Add to cart” buttons” that you will find in the ‘general options’ tab.
You can also decide not to show prices on ALL products, by enabling or disabling the “Hide prices” option.
This way, only a “Request a quote” button will be shown, and your customers are able to ask for a price estimate instead of checkout directly.