So, I spent last night figuring out how to make fonts using Inkscape, there have been several messages on this before, so they probably know this already.
Fontforge does things in terms of sub-em units. Traditionally, TrueType fonts are 1024/2048/4096 sub-em units, and when FontForge reads SVG, it uses the pixel as one sub-em unit. Since I was creating a mono-spaced font with 4096 sub-em units, I created a canvas that was 4096 pixels high, and my fixed width wide. I placed guides at the baseline, x-height, and capital height to allow easy repeatable placement of the letters. From that point on it was easy copying from my source file, saving the individual glyph and importing it to FontForge.
As far as things in Inkscape go, one thing stung me several times. I expected Center on Drawing to remove the current selected objects from consideration prior to computing the center. I can't imagine why you would want any other behavior?