... you could use this rim you have for practice if you feel you would risk things when building on a new rim.
i would advise to change the spokes too for a new rim or for different spoke cross etc. dunno about what gauge you would choose but be sure to pay attention to spoke being vulnerable to plastic deformation by torsion. butted spokes more so.
http://www.tribology-abc.com/calculators/e3_6a.htm