Quick Q about Mithral armor and lack of proficiency

[Tinculin]

If a bard dons a mithral breastplate and lacks the medium armor proficiency, i'm right to assume that he gains the full ac benefits, can still cast spells (because mithral means its treated as light armor except for armor proficiency feats), and is at a -1 maneuvor penalty which also translates as a -1 to attack because he lacks the medium armor proficiency.

The bard then picks up a mithral heavy shield and receives a 5% arcane spell failure but no further penalties as the mithral bonus counter acts the maneuvor penalty.

Providing the bard can find a way to offset the -1 man. penalty from the BP (spell/item etc), he can use both without any penalty, only a 5% arcane spell failure and without needing to dip levels to take feats?

Correct?

[Malkavian_Andi]

Almost correct. A bard doesn't suffer spell failure from using shields.

[Gwaihir Scout]

The Armor Expert combat trait reduces armor check penalties by 1. Take that and you're golden.