S5 Phone and SD Card Encryption: Do I need to enter in password twice?
No. I have that setup and you don't need to enter the password two times. Also when encrypting, android (at least my 4.2.2) does not let you use different passwords for Device and SD card.

One downside of having the phone encrypted is that Android forces you to use the encryption password in the screen lock. After encrypting the phone, you can't use pattern unlock. This has been reported two years ago.