>immediate problem of why I can not edit this mesh
I would start with geometry that is far less complex.
In order to edit geometry you should have native sketches and solids/surfaces.
There are other programs that are more suitable to edit the mesh that you have.
You can create some complex geometry in Inventor (see attached image) but you need expert level experience.
My students start out with a beginning geometry using AutoCAD, Inventor, SolidWorks and Pro/E 5hrs/week for 16 weeks. Then they take a surfaces class using AutoCAD, Inventor and SolidWorks for another 5hrs/week for 16 weeks to get to the level of creating attached and this link
http://home.pct.edu/~jmather/content/DSG322/Student%20Gallery/Dogging%20It.jpg
There is no Easy Button.
Inventor is more than an art tool like some of the other software you might have used.
If you want more information on using neutral format geometry you might try this
http://www.myvbooks.com/ac55jsp/stores/1/ML205-1P_Working_with_Neutral_P309C98.jsp
but I don't think it will really help you and I'm not sure you are ready to get anything out of the "book" that could help.
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Autodesk Inventor 2019 Certified Professional
Autodesk AutoCAD 2013 Certified Professional
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