1) is it possible to specify the fonts in an MPenviroment? If so, how?
Just as you will specify fonts in your regular document.
Putting the same definitions inside \startMPinclusions... \stopMPinclusions does not seem to work with XeTeX.
It is MPenvironent and not MPinclusions. I do not have xetex, so I can not test this.
Ok, even if I put those definitions in an MPenvironment the text fonts do not change (I guess the mechanism for font selection is slightly different in XeTeX).
how do I change
\startTeXtexts \dorecurse{10}{\TeXtext{\recurselevel}{$x_{\recurselevel}$}} \stopTeXtexts
so that I can print labels from x_0 up to x_9? Do I need to use \defineconversion and \convertnumber?
No, use \dostepwiserecuse. The general syntax is
\dostepwiserecurse {from} {to} {step} {action}
so
\dostepwiserecurse {0} {9} {1} {\TeXtext{\recurselevel}{$x_{\recurselevel}$} should work.
Thank you very much! Nicola