OK, thanks for some more clarification.
First, I believe there is an Office 365 (I assume that is what you meant, even though you typed Office 360) "version" for Macs (here is one available at Amazon:
http://www.amazon.com/Microsoft-Off...6969&sr=8-9&keywords=microsoft+office+for+mac). Again though, for me, Office 2011 is good enough. And, Outlook 2011 has never caused me any issues.
As for Google Chrome, I never got any spam EMails from them once I started using their browser. Maybe that is a "Windows" thing! I did, though, have one strange virus "issue" with Chrome a few months back, but only on one of my Macs. I did get it successfully resolved (thank god I use SuperDuper! for my backups! I'll get into that somewhat below).
Now, backing up to a 2 TB internal drive is just about as good as backing up to an external drive (as long as all the internal "connections" work!). Given that you'll have just about all your "stuff" on the 256 gig SSD (Yosemite, Applications, etc.), it depends on what "kind" of backup you want. Apple does supply the free Time Machine backup software as part of the OS, and you can easily schedule it to run as often as you want. But, it does not create a
bootable backup, so quick and instant recovery is not going to be the case. You can eventually recover all the non-OS "stuff" from such a backup, but you would first need to re-install the OS. The other type of backup you can make is to use backup/cloning software like SuperDuper! or Carbon Copy Cloner. Either of them makes an
exact bootable backup/clone of everything on your 256 gig SSD (I assume that is what you primarily want to backup). So, if you have a bad "disaster", you can boot your Mac Pro from that bootable clone, erase, format, and if necessary, partition the 256 gig SSD, and then do a complete restore from the backup/clone. For either product, you can also have scheduled backups, just like Time Machine (I don't need to do that, as once a week backups are good enough for my purposes). SuperDuper! costs $27.95 (it's the one I use; here is the link to their site):
http://www.shirt-pocket.com/SuperDuper/SuperDuperDescription.html),
and Carbon Copy Cloner costs $39.99 (here is the link to their site):
https://bombich.com/
One advantage of Carbon Copy Cloner (if you need it) is that it also backs up/clones the invisible Recovery Partition that the Mac OS makes. For me, that is not a detriment (by using SuperDuper!), as I have two excellent disk maintenance/repair programs. Also, there are a couple of ways of re-creating that Recovery Partition. This link explains what is on the Recovery Partition, and how to boot to it (a slow process):
https://support.apple.com/en-us/HT201314
For disk maintenance/cleanup/repair software, the free program Onyx is excellent (although limited in what it can do)! I have been using it for so many years, and it has never failed me. Here is a link that discusses it (you'll need to insure that you get the correct version):
http://www.titanium.free.fr/
When you click on the Download button, the next page will contain the versions available. You'll of course want Version 3.0.1, as you are using Yosemite.
Onyx is primarily beneficial for 1) Repairing Permissions, and 2) cleaning out unneeded "crap". But, for actual disk maintenance/repair software, either TechTool Pro (
https://www.micromat.com/products/techtool-pro) or Disk Warrior (
http://www.alsoft.com/DiskWarrior/) are
excellent! I have both, although an older version of Disk Warrior. I use TechTool Pro as part of my weekly cleanup/disk maintenance/repair (hardly ever need to do repairs) and backup processing for both of my Macs. Again, I have been using it for so many years. and it works great! It has so many useful features.
Just to let you know, here are the steps I go through every Saturday for both of my Macs:
1. Permanently get rid of Deleted EMails in Outlook (Microsoft provides a way to do that).
2. Run Onyx for Repairing Permissions and some disk cleanup.
3. Run Tech Tool Pro for more extensive disk cleanup/maintenance (and if ever necessary, repairs).
4. Run SuperDuper! to do two backups/clones for
each of my machines to two separate external drives.
By doing all that, I rarely, if ever, have issues with my machines. (I am actually doing other chores while all that stuff is running, ie, I am "multi-tasking"). The neat thing about Tech Tool Pro is that it creates an eDrive on your internal disk (SSD in your case (I also have 256 SSDs in side both of my Macs)), and I can boot (re-start) my machines from that eDrive, so that the disk cleanup/maintenance is just like doing it externally, which is necessary for trying to do maintenance on the internal/boot drive. (I understand the new version of Disk Warrior has something similar, but with the SuperDuper! backup/clone, I have an external "way" of running Disk Warrior).
Finally, for watching movies/videos, there is the venerable free software VLC (Windows version also available). You can get it from here:
http://www.videolan.org/vlc/index.html
Sorry for the long post, but I wanted to try and answer all your questions as completely as I can. One other thing: are you using the latest (and last) version of Yosemite, V 10.10.5? Let me know, as I can provide a link so that you can upgrade to it easily.