Hi @fgilio - I’m in a situation where we have a managed WordPress host, who places a premium on storage. They use 2n + 1 HA for storage + offsite copies, so they charge a fortune per GB as each file you write is replicated 2, 3 or 4 times, so we too are looking at offloading to S3 (and the Delicious Brains plugin was the most attractive for us).
I guess the scary thing is: for it to be effective, you have to take a leap of faith in deleting the images from your web server, and then serving them only from S3. The reliability of S3 itself isn’t a problem for me; it’s pretty robust, and if you enable versioning, you have roll-back options. The issue for me could be the rewriting of URLs, and having faith this would work with all of the other moving parts of a WP site…
The other consideration for us is that when we draw up contracts for clients, we have to tell them: part of your site is on this super secure cluster with 2n + 1 HA, snapshots, off-site backups, x hour SLA etc etc, and then other parts of your site aren’t (ie some is on the web server, some is on S3). It’s not a problem, but just takes some explaining.
I have now found a plugin (Imsanity) which will resize images in the media library to fit within certain dimensions (which you could use in conjunction with EWWW, I guess), and I have updated my terms of service to say that images on the web server are for web use, and the web server isn’t a file repo. Images may be resized to these dimensions (which currently is a max of 2000x2000), so please ensure you keep the originals. I believe the plugin can also resize images on the fly as and when users upload them.
Whether this hard-line approach is for you, I don’t know - but I am very transparent about it, and explain the reasons and have had no push back so far.
I reduced 21GB yesterday to 5.5GB by doing this…
I still have to figure out a way of dealing with PDFs though 
With regards to the S3 offloading, I would be inclined to go with Delicious Brains, and pay for support. As @darjanpanic said, their support is great (I use Migrate DB Pro and when I had a few niggles using earlier versions, they would go above and beyond to sort it out), so if you do go down this route, at least you’ve got some backup with them.