Blender isnt linux only, you can get it on windows and mac pretty much the same way, the only problem is actually being able to use it for srb2, which im pretty sure the one .md3 export addon is for an old and might not work in newer versions?
Maverick though supports .md3 and .md2 out of the box, though it's more limiting than blender, and makes high-poly really hard. I'll give you some tips about that one though since it's the modeler I actually use.
Dont use Misfit, it sounds different but it's litterally the same modeler but worse.
Cylinders are your prisms pretty much, theres an option when making one to give them a certain amount of horizontal sides, so if you want a triangular prism you would put 3, or for a pentagon 5.
You can also make a "segmented" cylinder, creating a certain amount of edgeloops without you needing to go in and extrude it yourself, it's also really great for joints when animating
Moving things around and rotating act differently when holding shift, both cases being to the great benefits of precision
For moving this restricts it to the first axis you make your mouse move along, super sensitive though, you're gonna have to undo it if you accidentally move your mouse a couple pixels down when you first move.
For rotating it only lets you rotate to specific and exact angles, like 45 degrees or half of that, can't tell you how many times i've used this, as I'm one to get these rotations nice and perfect and well, that's something you would never be able to do with regular rotation.
For texture mapping, you're just moving verticies around in a 2d plane, all the tools for that would be on the right side of the window, buuut you will have to deal with resetting the camera every single time you undo something.
One thing you'll really need for texture mapping though is resetting coordinates, which takes the view of it you'd get from a certain orthographic angle, and stretches it out onto the the texture, which is really good for gradient artstyles, and also like, actually getting textures to map normally.
Also like, watch your message board threads, it's kinda in the top right, it'll notify you when someone says something in that thread, which is good for help threads since it can mean you got help, or at least some
I have tried Maverick/Misfit for making models. Maverick is good for model making its just the pain to make a texture mapping for it. Mainly since md2s require one texture on all polygons (i think).
And my Chromebook running Linux is the only device I can run Blender on (even though it makes no sense at this point since it is crap on there anyway)
Blender had an update that made it only compatible with Windows 8 and up, and I run Windows 7 and macOS 10.12.6