Unless it's part of your character, I'd forgo shield bashing and twf. You have three feats in the iron tortoise feats which I know nothing about but that seems rather expensive and I imagine is doesn't pay off too well. You sacrifice decent frontliner feats like weapon focus and power attack just to hit with a sub optimal weapon. It could work if you are using a reach weapon and only bashing as a back up but you don't have the feats to pull it off. Is the heavy shield the character or optimization? A tower shield is the best "tanky" option but a buckler can you let use your hand for healing and what not. If you heed my advice and not go the shield bash route you won't need a heavy shield. Typically a healer picks up the extra channel energy feat but I don't know if the medic has channels or magic at all.
If you are going Aasimar I'd consider Angel Wings though that activates way late and has a feat requirement. Getting flight would add to your angel of mercy angle but the earliest you can get it is 5th level with Tengu Wings and racial heritage, not too thematic since a half crow man would look disgusting rather than angelic. Flight paired with a mithral breastplate would be stellar but it isn't to tanky.