Moved from the Creative Cloud to the Premiere Pro forum. They will be able to help you here.
>what sequence should I choose
To match your sequence to your video for editing...
For CS5 and later, the easy way to insure that your video and your project match
See 2nd post for picture of NEW ITEM process http://forums.adobe.com/message/3776153
-and a FAQ on sequence setting http://forums.adobe.com/message/3804341
>external hard drive
If that is a USB2 drive, it is not fast enough for video editing
External eSata or USB3 are both fast enough for video editing... eSata is better -
And, for future reference, the information you need to include when you ask a question
Information FAQ http://forums.adobe.com/message/4200840