What you want is:
1. A system that backs everything up
2. A system that is 100% bulletproof
3. A system that is easy to restore
The best way to plan it out is to create use-case scenarios:
1. What happens if your computer gets eaten by a virus?
2. What do you do if your boot drive dies?
So this is what I would suggest:
1. A system that has a bootable restore tool
2. A system that does automatic scheduled backups
3. Spare drives for your boot & data drives
It sounds like you already have a couple of useful spare 1TB drives, which can be used to replace either your 250GB boot SSD or your 1TB data drive. You mentioned you already have a 5TB external drive. So for the actual implementation, here is what I would recommend: (in addition to what you have already)
1. A copy of Macrium Reflect backup software
2. A copy of Malwarebytes antivirus software
3. A USB stick
4. A USB backup drive
5. A calendar system
Macrium Reflect v7 is $70 for a home license:
https://www.macrium.com/products/home
This allows you to do several things:
1. Create a full backup image of your boot & data drive
2. Create incremental backups of that full image (for quick daily backups)
3. Create a USB boot stick
When you install Macrium, it will prompt you to create rescue media. It will download WinPE & let you create a bootable USB stick, with drivers for your computer. You can use that USB boot stick to boot up your computer & select a backup file to restore. In your case, that would either be the last incremental file from the previous night, or if your external backup got eaten by a virus or failed, then it would be your monthly full image backup.
I also recommend a good combination anti-malware, anti-virus, anti-cryptolocker system. Malwarebytes is excellent for $40 a year:
https://store.malwarebytes.com/342/purl-consumer-pricing
However, Malwarebytes doesn't protect you from drive failure, which is why backups are important. So let's say your boot drive does. Your procedure would be:
1. Swap out your boot SSD with one of your spare 1TB drives
2. Boot up the computer using your USB recovery stick
3. Select last night's incremental backup file from your 5TB USB backup drive & restore it
4. Boot up to the 1TB drive like nothing ever happened
I should also note, Macrium v7 is new & has a special super-fast incremental backup feature. I am doing twice-a-day backups at some locations & am testing out hourly incremental backups for a couple heavy DCC users. The backups are VERY fast & with a 5TB USB backup drive, you'd easily be able to hold months of incremental backups on that.
But lets say somehow a virus does eat your boot drive, data drive, and USB backup drive. Or lightning hits your house and fries everything plugged in. Then you can grab your monthly full image copy (offline version - unplugged, on a separate drive) and restore from that instead. FWIW, you can now buy a palm-sized 5TB USB-powered drive for $140:
https://www.amazon.com/Seagate-Backup-Portable-External-STDR5000100/dp/B01LZP2B23
Last piece you need is your calendar, mostly just for remembering to back up to that unplugged drive. I'd suggest weekly over monthly, given how critical your data is & how important getting back up & running is, and how big & cheap the portable drives are these days. Without that calendar entry, you will eventually forget because you are not being reminded to do it.
So my recommended setup for you is:
1. Malwarebytes (anti-virus, anti-spyware, anti-cryptolocker)
2. Spare drives (to replace your boot & data drives should they physically die)
3. Portable backup drive (for offline full image backups on a regular basis)
4. USB stick (for emergency booting in order to restore a full or incremental backup image)
5. Macrium Reflect Home Premium software (for automatic scheduled incremental backups)
Testing your backups is also important, which is another reason I recommend having a calendar - you want to make sure your backups aren't defective (it happens). You can do it 3 ways:
1. Macrium lets you mount & browse a backup image (full or incremental). Generally, if you can mount and browse and open files off the virtual drive, then you are good to go. I would calendar this in once a week to verify.
2. You can restore your most recently backup to one of your spare 1TB drives & then boot to it temporarily just to make sure that your backup is fully bootable. If you are really serious about needing to get back up & running in the event of a virus or drive crash, this is probably your best option.
3. Macrium includes viBoot, which lets you boot your backup image straight into a virtual machine. If you happen to be running Windows 8 or 10 (or Server 2008/2012/2016), then you can install Hyper-V, which is like Microsoft's version of Virtualbox or VMware. Then you can just boot your backup straight into a VM to check to make sure everything is working okay. That's a nice zippy way to check functionality of the backup, without having to actually do a hardware swap.
I will tell you 3 horror stories about backups:
1. Just today, I had a user who needed to do a simple task - format an SD card. For some reason, he kept his files on a MicroSD card, plugged into a MicroSD to SD adapter in an SD USB adapter in the back of his computer. He stuck his new SD card in the front of the computer and proceeded to wipe out his backup/data storage card. Oops. And of course, he didn't have a backup. Fun times were had (sic) after that using recovery software.
2. I have a friend who is a photographer. Hundreds of thousands of photos. Liked to use a combination of backup services, but in a scattered way...Smugmug, Crashplan, etc. Her iMac's Fusion drive recently died (SSD/HDD hybrid). Restoring was...an arduous task. A lot of organizational metadata was lost, and there was no way to verify that we recovered 100% of her stuff. Even though she was also using Time Machine, but had only selected specific folders for it to back up. It was a huge mess because it was a complicated backup system. If she had had a simple backup system, it would have been a piece of cake. Side note, I also HIGHLY recommend Backblaze, which is an online, encrypted backup system with unlimited storage for $5 a month. It is GREAT if you know what folders you want to back up:
https://www.backblaze.com/
3. This one will give you a nice pit in your stomach - the story of how Toy Story 2 was almost lost during production. Watch the whole thing here:
TL;DR - it is long to write out, but the idea is simple: make it easy, and make sure you protect yourself properly. It is not hard to do. It does require some up-front setup & initial financial investment into the software & hardware required to make a truly operational system. Most of it is automatic; your calendar can tell you when to (1) do a full system backup to an unplugged backup drive, and (2) when to check your backups manually to make sure they actually work. This creates a fairly bulletproof system. I setup systems like this for customers both in the corporate & individual world and it works great. It is not fun to have to spend money on this, nor is it fun to have to follow manual procedures on a weekly or monthly basis to test & back things up, but if/when Murphy's Law does hit you, it will be worth every penny & every moment spent having to check & run your backups.