You got some valid points, but those can be explained quite easily :
- Pepper can walk in the armor, which shouldn't be difficult at all, but she can't use it. Noticed how she couldn't control the repulsors ? See, she couldn't really use it, just move in it. With the exception of Pepper blasting Killian at the end, I put that on the extremis treatment she got.
- It's not the address giving that triggered the attack, it's the threat Tony made to the mandarin.
- His previous suits could indeed take a lot damage, but the MK42 is only a prototype that is not combat ready. Jarvis said it. It is purely to test the new assembling method. Therefore it has a tendency to fall apart when taking heavy hits, especially when it's empty.
- that wasn't said in the movie, but it is in the comics : at one point medical science got good enough to remove the shrapnel from Tony's heart without killing him, this wasn't the case before.
- all the suits have integrated batteries, how else do they work on their own ? The arc in Tony's chest must serve as an alternative power source, though I imagine that nearly dying in IM1 after emptying his own arc, he now prefers not to use his own too much.
-extremis soldiers can withstand a lot of things, including severe burns and lost members from explosions nearby them, but once they explode themselves they are dead, disintegrated. That's why they never find explosive devices, there is nothing left. Don't know where you got the idea they can explode and live.
- the president can't use the armor, he's trapped in it while AIM controls it. The only guy that seemed to kinda use it was Killian's henchman in the plane, but even him I'm not sure he knew how to use the weaponry, since he just punched people or shot them with a normal gun.
-He goes on about caring more for her, not exactly protecting her, what she wanted was to spend more time with him. Plus he will make at least one new suits in the future, that's what is implied when he picks up the screwdriver and the two robots in the trailer of the R8 e-tron. He's just not going to spend his all time building 40+ suits on the basement again.
What I can't explain neither is the weakness of the suits other than the mk42. Quantity over quality ?