To change the speedline font just find the entries for FontName="Speedline" in the styles.xml and change them to FontName="WhateverFontYouWantToUse". Should be 2 or 3 entries. That changes it for all the interface. Same for the other fonts.
Tooltip font size might be somewhere in the options, otherwise you'll have to modify the respective tooltip windows.
But frankly, if you just want to enlarge everything due to bad eyesight I'd suggest to simply reduce the game resolution until everything is big enough. Or buy a bigger screen.
