This is really important to setup the integration tests as soon as possible. I've seen so many developers which were trying to do it in the middle of project lifecicle Just imaging how many problems they faced at that stage: complex DB scheme, authentication, authorization, billing system and etc. At that point there is no chance to do it quickly and cheap, so weeks whould be spent just to have a simple test.
Hooking up Travis CI/Gitlab CI to the Github never been easier.
Generating dev data
If you are building a UI take care of preparing mock data so developers will be able to do their work without any dependencies on actual backend side. For backend development create a data generator or some fixture files. In more advance case, for example to debug PROD issue, which is not reproducible on staging, think about creating a special tool fro copying production data with stripped confidential information.