[XeTeX] Issues in using the Book style in Xetex

[Faisal]

Hi Xetex members,

I am trying to use Xetex to write a book in Arabic language. I have
used the example-arabic.tex template in Xetex(
texmf-dist/doc/xelatex/polyglossia/example-arabic.tex). But, I got the
following problems:

1- The chapter name is the standard one in Latex, ie Chapter 1 so in
arabic it will be الباب 1. I want latex to print first (or الأول),
second (or الثاني) instead of the numbers 1 , 2 etc in the chapter
name.

2- I have created a new environment called example using
\newtheoremstyle{example}{12pt}{12pt}{\bfseries}%
{}{\rmfamily}{:}{\newline}{}
\theoremstyle{example}
\newtheorem{example}{$\square$ \underline{مثال}}[chapter]

But, the problem is that the vertical space between the enviroenment
name (مثال in this case) and typically one line. How can I make it
double lines or more.

Thanks in advance for your help.

Faisal