That's how the stock Google launcher is designed (to get to search quickly). You cannot change it.
Also you cannot disable the Google app as it is a system app like @Tinkerbell91 said. But you can try something - uninstall the updates for Google app and there are chances that you can see the Disable button. I've done that before and it worked. BTW I got the same mobile.
Regarding the Home screen use can use other launchers from Play Store. I use Nova Launcher which is very close to stock launcher and provides you to customize the appearance. That is my choice but you got numerous options out there.