Do you I think I should integrate something like AWS or other cloud service from the initial phases of my project or I should be working on the front and back end components regularly and integrate AWS later?

I am starting to work on a mobile service. From day one, I wish to make sure that my service will be scalable and able to handle large loads of requests. This is my first time in architecting a large scale system from the beginning so I can't decide what is best.