How do I create a plane through 3 points using points on a mesh?

[NotJordansime]

Hello,

I have an STL of an Otter (aircraft) that I need to split so that it can be 3D printed. I first tried converting the model to a body, but this crashed fusion 360 every time. I then tried using construction planes to split the model where needed. Problem is, I'm having trouble aligning the planes to points on the model. When I try to use the "plane through 3 points" feature, the only point it lets me select is the origin. Can I manually add "vertex points" to points on the mesh where they're needed, or is there some better way of doing this? 

The image Otterside shows where I would like the plane aligned. The image otter3points shows where I would put the points if I was able to place them at vertex edges on a mesh. The video shows that I am only able to select the origin as a point for my plane.

Any help would be greatly appreciated, as this is a gift for my friend's boss who is retiring soon. 

[jeff_strater]

You can sort of do this, in the "Edit Feature" mesh environment.  You cannot snap to mesh vertices, but you can pick a "mesh point" which is on the mesh, and you can get pretty close by zooming in.  Since meshes are fairly inaccurate anyway, often this is sufficient.  See the screencast below:

https://knowledge.autodesk.com/community/screencast/f8f5b784-737a-4a05-89b4-52886328e63f 

[JDMather]

@NotJordansime 

Can you Attach the original file here?