Install application in SD card or external USB drive without root? Is it possible any of the following in a non-rooted Android device?


Install an application "manually" (without using Android Market/Google Play)
Install an application in an external SD card
Install an application in an external USB drive connected to the device
Yes. See: Can I install apps on phone without using the Android Market? 
You can't install directly to the SD card. In many cases you can move much of the app and its data to the SD card, but the OS and the app have to support it. Even then, you need to install normally and then move it, and you can't move 100%.
Not without a custom ROM, and maybe not even then.