Inkscape isn't a great tool for font editing. It cannot load or save font files in the common formats. It can save SVG fonts, but it cannot read or use them.
You could type out all letters in Inkscape, then follow a tutorial (like this one:
https://ahninniah.blogspot.de/2013/06/c ... scape.html) to create an SVG font, then convert it back to an otf.
However, I'd rather suggest you learn how to use fontforge (
https://fontforge.github.io). It's going to be a lot less work, and it will be faster, and allow you to just 'edit' the font, instead of converting it back and forth.