Disable payment and shipping options

Is it possible to be just able to add products to a cart without payment and shipping options?

I will also like to add "add to cart button" on category listing page

You can remove shipping by setting all your products to need shipping. Payment however you cannot remove, though you can use Cash on Delivery for example to allow a quicker checkout

Does the lastest version of opencart allow for 1 page checkout?

Yes it has a one page checkout, however it's still panel based, so it loads one section at a time