i recently bought an external 4terrabyte HD and Acronis 2015. Then I backed up my entire system, unplugged the drive and kept on keepin on. I figure I've made enough new changes and bought enough new plugs to do a new backup. Do I just plug in the drive and do it all again...or is there something different I need to do in Acronis to just "amend" the original backup??

In the version I run Olpal, 2011, there is an option to either incremental backups, i.e. the differences or to do full backups but to keep the last two versions or as it was called Grandfather, Father, Son.
 
The differences version can be a little more difficult to restores as you need restore the master then the differences but takes less time to do the backups.

I'm done backing up, time to move forward! 

Hi,
 
In the old days, at mom's office, we did a master on Sunday and then incremental backups every day to ensure no loss of data. Luckily, and surprisingly enough, we never had to worry about data loss as far as I am aware from my time there. And the backups were all dated and marked properly and in the right place locked up.
 
At home, I always used "incremental" backups, but since that time, I do my backups on the files that I need to different drives manually so I have the copies of the work. For me, installing/reinstalling the programs is not an issue, and chasing down the right back up to get the proper piece you missed is more of a headache than it's worth.
 
Mind you, I'm not an admin, only a network at home for my computers, and that is vastly different, than an office! But simply doing images and restoring complete backups is too much of a waste of time. Mostly your "file/files" are not that big anyway, and should be easy to copy to your location.
 
NOTE: This precludes that you DO NOT allow programs to set their own location for files, because it will be all over your hard drive. All my files are in my own folder, split up in several portions so all I have to back up is that folder. I don't see the point of backing up all the doodoo from Microsoft Word, for example! Thus, I have a folder named "Files" and it has in it Writing/Poetry/Film/novels/short stories/criticisms //// etc ... etc and that is the ONLY place where everything goes. 

Ideally you should take it to another location in case of fire or theft.  I keep mine in a supposedly fireproof cabinet, which isn't quite as safe as keeping it offsite but still probably better than just keeping it exposed.  I've gotten into the habit of running a full disk image backup around the first of each month - easy to remember.  Again, not optimal - probably once a week would be better.  I keep as many backup copies on the external drive as will fit on it (three for my DAW machine).  I just delete the oldest one before running the monthly backup.

One thing that threw me off badly starting use Acronis was just that Incremental Backup.
Simple as I am, I figured the first backup can't be incremental, as there's nothing there to add something to.
But then, trying to do incremental backup on the first one, it wasn't possible. You need to choose the incremental mode in the beginning, only then is it possible to add only the new or changed data to the backup-string.
 
But in addition to that, I do manual per-file or per SONAR-project backups to be able to find the exact files I'm looking for. I find the "closed system" backups, where you can't separate individual files, quite unpractical.

Don't forget to create bootable media such as a CD and install all the updates.

With a 4tb drive, I'd just do new backups as you have plenty of space. After they're are year old or so you can decide if you want to keep the oldest

And the acronis cd can be your bootable media too

I've got about 3.5 TB to backup.  So it takes almost that whole drive to do a complete backup of my system.