How to make an armored wizard?

[Corran]

I have an image in mind, that of a necromancer wearing some metal armor. Anything from as 'low' as a breastplate to as high as a 'fullplate' would fulfill the stylistic criteria I have set, so I have some room to move freely regarding building this character.

So, how would I best go about it?
Should I grab a fighter or cleric level for the proficiencies or is it better to grab the feat giving me armor proficiency?
Would I be better off with a medium armor so that I don't have to take many of the feats that drop the chance of spellcasting failure due to wearing an armor? What metal armor would be the best to pick?
If I multiclass 1 level in fighter or cleric for the armor and weapon proficiencies, how much of a disadvantage would it be to pick a race that has none of fighter, cleric or wizard as a favorite class? Meaning, do you really feel the xp penalty or is it something that I might even forget?

Thank you in advance!