More a general questions aimed at those who have installed Nextcloud on AWS or similar. I’d be interested in knowing what your experience was, as I am giving up on my QNAOP NAS (because of the constant threats to it).
Also, curious to know what the cost base is like say 2-3 TB max
Thanks in advance
Gerry
Maybe this is of any help…
There will also be threats against it, when you host it on AWS. And most of the things you have to do to mitigate those threats now, also apply if you host it on AWS. Hosting your applications on a cloud platform does not automagically protect them from all threats. I know that was not your question, but I wanted to mention it… 
AWS costing is a tough one to estimate and know in advance that monthly costs can be punishing.
Initially our small business had a basic i5 desktop running as a server and we decided to move to AWS when our Ubuntu Server LTS version was near end of life. When we moved to AWS we had two web apps (400GB EC2 and 120GB EC2) and one RDS (relational database). Monthly costs with limited web traffic was ~ $550 USD + tax. AWS’s billing is less than simple to understand and I ended up having a team from DigitalOcean review and they couldn’t make heads or tails of the invoice details.
After a little more than a year with AWS we decided to go back to bare metal and bought a new dual CPU Dell tower server with one XEON processor and plenty of redundant SSD storage. It was a big initial outlay but it paid for itself in about 8 months and we have a lot more storage capacity and computing power than what we had with AWS.
As for security, I agree with bb77. We implemented the same security protocol when self hosting as we had under AWS. There is no magic bullet for security when switching to the cloud.
I agree about threats but let’s say QNAP is beaconing a liability. It’s up for sale 