How to edit an Inkscape file in Adobe Illustrator while preserving the aspects (fonts/placement/etc.) of the original file?

I created a poster in Inkscape, but the person I created it for would like to edit it in Adobe Illustrator. The Inkscape file (saved in both Inkscape SVG and EPS format) contains text, images and paths. The text is made with fonts that were downloaded from an external source and are not normally found within Inkscape or other applications.

How to create a vector curve programmatically?

I want to create a vector curve that is symmetric in the top and the bottom. For example, in this baseball icon (How to draw a baseball in Pixelmator?), if I try to write the vector as suggested by the accepted answer, I end up in writing the vector curve by hand – which means the curve can never be symmetrical between the top and the bottom.