Start with Blueprints. I spent two weeks trying to do this in C++ and got nothing except headaches and crashes. Check out some of the procedural tutorials for the basics. The first 20 minutes of this showed me the way. https://www.youtube.com/watch?v=mI7eYXMJ5eI
This might not be entirely UE4’s fault, I’ve been working with C++ for less than a year, and dealing with new libraries is a big weakness. Still, it’s clear that UE4 has been designed to support Blueprints first-and-foremost. Manipulating an object took most of a week to get working well, but it wasn’t too difficult. Doing that and more (object spawning and manipulation) with Blueprints took a few hours, and was quite easy.
I still haven’t found a great solution for spawning lots of objects with different color materials, all defined at runtime - but Blueprints seem to be the way to go there, too.
I tried unsuccessfully to find Particle creation and manipulation through code (which is super easy in Unity), though by the time I switched to Blueprints, I had set that tactic aside, so I’m not sure if that’s easier to accomplish with BP. Depending on how your several million points break down (e.g. is it several million total, broken down into XYZ, RGB, Scale.XYZ or is it several million points, each with their own XYZ, RGB, and scale) it might be too much for UE4 to handle - unless you’ve got a really powerful machine. Particles would almost certainly be more efficient. If you just want tris, I’d look into Panda3D - which is an ordeal in itself, but has significantly less overhead for simply rendering several million of them. To be sure, I’m not promising it will be easier than UE4, but it will almost certainly be more efficient for doing the same thing.
This also might help for the UE4 route. Several million data points might be a little much for excel - creating a csv file automatically from your data should be less of a problem. Whether or not your machine can run the results well, that’s something else.