So the main point seems to be MS has killed modern.ie -site and redirect to this dev.windows.com site. Still useful once in a while although the big disk images are PITA to download and setup. I have better uses for my laptop SSD than to fill it with different IEs and Windowses :p
Depending on your model of laptop, you can probably get reasonable speed from expansion storage for rarely used images like these.
I opted for the 128GB SSD in my MBP (last 17" model, from late 2011) and a few years later I added a 128GB ExpressCard SSD, which i use pretty much exclusively for (largely Linux, largely via Vagrant) Virtual Machine images. Sure, I'll definitely order a bigger built-in SSD on the replacement, but on a newer machine without ExpressCard you could also use a USB3 flash drive or (if you are on a mac) a Thunderbolt SSD device.
I have plenty of disk space but my photography hobby is eating most of it and the first thing that gets thrown away is the 14 Gb vmdk (this time it's Windows 8.1 + IE11).
Next one is probably 8 gigabytes of MS Office 2016. How can Office eat 8 gigabytes? :D (Compared to LibreOffice's 700 Mb or Office 2011 1,3 Gb.
And why worry about the new IEs and Edge? Microsoft says they support standards and so forth ... ;-D
Those are only available for the 2012 and early 2013 Retina machines, the first two models. You can also get an mSATA adapter on eBay and use any mainstream mSATA drive to upgrade those which is even cheaper than the OWC drive.
There are tools for this.. iirc BrowserStack is a service on top of Selenium WebDriver, and there's tooling for it in the node ecosystem. IIRC, there's decent Ruby tooling, but I prefer to do all my browser related things in JS.
I setup a server with 16GB of RAM and a 480GB SSD, and installed 2 of each of these on the machine using VMware ESXi (the free version)
At the time we were supporting XP+IE6 for a client so this worked great for testing older browser versions, and prevented each developer from having to install their own local copies. Just RDP over to the test box...