Yes, there's some parametric things you can do in Blender. You can have a beizier curve that you can later change the facet count on... and you can use a spin modifier on a shape, but you're not going to get a perfect tangent line off a perfect circle like you can in a proper CAD tool for example.
and you can boolean with another object, are you're not able to add a perfect fillet at that intersection.
In Blender, with care and if you're clever, you can do many of the same things you can with a CAD program... good enough for many cases. But Blender is still more of an artist tool than an engineer tool. For serious uses you're going to run into the limits.
There are free cad parametric modelers. FreeCAD is one.
You can use Blender for some CAD work... But it's not a solid modeler like solidworks/inventor. It doesn't have many of the precision and parametric tools.
Blender's internal representation of objects is vertices (defined with IEEE single precision floats) connected by lines, and faces --just the shell of the object, and no real curved surfaces (just more and more faceted to approximate curves, and smoothed normals to look curved.) It also does not have guaranteed precise measurements. Blender can do some parametric and Boolean operations and many of the same things, but sometimes it fails and the limitations get in the way.
Some have built CAD tools into Blender, but it's a hack on an artist's tool. For some types of CAD projects, it'll do great, particularly in some very creative directions, but I'd start with the other tools you mentioned.
I export Inventor models to Blender for better rendering and animation.
"Merge doubles" is renamed "Merge vertices" (alt-m) > "by distance"... in the "Vertex" menu.
(Though the change makes sense to me, I wish they kept an alias so people can still find it.)
It bends over backwards to be discoverable for new users, but it's still a powerful 3d program with many features... an understanding of those concepts are needed to make any 3d tool to work.
There's already a ton of 2.8 video tutorials: https://www.youtube.com/results?search_query=blender+2.8+tut...
It still has the powerful tiling window system. There's no overlapping windows so you don't close windows, you combine and subdivide windows to make the tool layout you want.
But now there's Tabs for different default window setups:
Layout, modeling, Sculpting, UV Editing... So you shouldn't have to change the setups much, they're already designed for the task. You can can still customize/ create your own. That feature was already there as a drop down but now it's more accessible and you can add more default layouts.
UV editing has a tab at the top now. There's a few things to keep track of to be successful with this tool and hook up with materials, but I don't think the difficulty is much different then similarly powerful tools. There's youtube tutorials that will walk you though it.
Yes, Eevee is a fast pbr renderer and can give very similar results to cycles with no effort, except there's some setup needed to do indirect lighting and reflections... and some tweaking needed for good lamp shadows in some cases, but the payoff is huge. I have a high resolution render that takes 12 minutes in cycles, 30 seconds in eevee with no grain... some features are not there line a shader bevel, but otherwise very similar, and there's workarounds for that.
'Too hard to learn' was a legitimate concern in the early days... even though the payoff is huge. Perhaps it still is some, but not more than most other 3d suites. The interface is so much discoverable, and has switchable key maps so that it's similar to other 3d apps.
Perhaps a crawler can find the identical file (checksum/md5) and collect meta data: alternate filenames, urls, zip archive names... It was next to this file in this list/zip archive... And in this sub folder name, on this page on this wayback machine link... So associations can be built automatically?
Also for each unique checksum with listed alternate file names,
Perhaps user content: ratings, similar files, comments... A wiki like page where the automaticly generated meta data can be vetted...
Oh and suggested sound font and other settings to play that particular file maybe.
I'm voting up all the https://scratch.mit.edu suggestions. I was active in that community and with the developers early on. I wish I had it when I was little.
You can browse projects with the 5 year old then view the source and figure out how they work. Show that they can change things.
It's awesome that you want to promote creation over just consuming content like most of their peers.
Scratch your own itch with it too. Make a 3d renderer or CRUD app, fractal explorer, or game... they might like to see what can be made and what excites you.
They may get into the story and animation projects made by other kids first, that's good too.
I used team viewer, but not sure if you can login without exchanging numbers in the free version. There's many others. Try this list:
https://alternativeto.net/software/logmein/
In Blender, with care and if you're clever, you can do many of the same things you can with a CAD program... good enough for many cases. But Blender is still more of an artist tool than an engineer tool. For serious uses you're going to run into the limits.
There are free cad parametric modelers. FreeCAD is one.