3D spiral stair case

Since it looks like you're already using Blender as a reference and already have the staircase modeled, you can actually export grease pencil outlines to SVG(another vector format)!

You will need to first create line art from an object, the entire scene, or collection if it's multiple specific objects you want to be outlined with add>grease pencil> (scene/collection/object) line art. The grease pencil can be tweaked to only project to where you want them if needed in the modifier settings (it's pretty good by default usually). 

Next, set up your camera to where you want it, change lens characteristics, etc.

Lastly, You will go to file>export>SVG and it will export an SVG file to your computer which can then be imported to Illustrator. 

Some things to note:

The grease pencil projects from the camera, but the exported SVG will be from the actual viewport, not just where you place the camera, so make sure you are viewing the active camera before export.

The paths may not be connected, so it might not always be as simple as drag>drop>color, and if not, selecting paths then right-click>join can sometimes work but more often than not, it won't, so using the grease pencil as a guide for your color blocks in a secondary color layer underneath the lineart is usually the best route. Also, locking the grease pencil line art layer to prevent accidentally connecting to incomplete paths is a lifesaver and will save you from so many headaches.

Just because the grease pencil lines within Blender are small or large relative to the object, doesn't mean the paths will be that way in Illustrator, so when you set up the grease pencil, the thickness scale should remain around 1.00 (equates to about 1pt stroke), but it can be changed later on in Illustrator itself, so it's not the end of the world if the stroke is too big or small in illustrator. 

I've attached an SVG I have previously exported from Blender and used as a guide in a project, check it out if you'd like, there are some imperfections, but makes an excellent jumping-off point, especially if you're well-versed in Blender!

I hope this isn't too late and this helps you out!