I used to work with a guy who was religious about backing up his files to an external drives. Until someone broke into his house and stole his computer AND his external drives. He lost everything.

It's always a good idea to have an off-site backup (e.g. in case of fires, robbery, natural disasters, etc). If you prefer to manage them yourself, an option is to find someone else who also needs an off-site backup and exchange disk space. You do your off-site on their machine, and they do theirs on yours. With external HDDs, you can just have someone else hold on to it for you at a different location. You can come up with fancier schemes to reduce the chances of data loss or to make the process simpler if you care to do so.

I also like local only with a similar set up as yours, rsync to and HDD and to an SSD.
But I also would recommend you to follow that suggestion, you need to have an external backup managed by someone else (encrypted, of course) so you can have options if anything happens to everything in your local.
It's up to you how much you're willing to pay to be sure to be able to retrieve your data.

I'm using iDrive e2, it says it has a limited offer, but it's been there for over a year.

Im basically paying $1.25 for 2TB per month (it's charged at once for 24 months) https://www.idrive.com/s3-storage-e2/pricing