Sorry, checked the wiki for madness mutagen values as i finished my only playthrough with a madness mutagen long ago and i haven't gone alchemy tree before(most of the skills are useless for me even on hard, maybe an insane playthrough will change that) so i also used the wiki for impregnation's effects on mutagens.

You can't say what is the optimal armor, because it starts really rising only in the middle of the game and especially at the end. I know that without armor potion and being intoxicated (for alchemy bonuses) I always got more than minimal damage. But in the end at full armor the endgame boss has dealt only minimum damage (certain gargoyles could still hit through this armor). And it did not protect against magic damage (there is an other stat for that)

I always chose armor over health no matter what, for these reasons:

- damage prevented doesn't need to be healed, a large health pool means you'll need more healing.

- still about healing: higher hp pool decrease the value of your healing, since the amount you can heal is a fixed amount of hp/seconds (depending on gear/potions). Larger red bar just means less %hp healed each second.

- there isn't enough magic damage in game to justify valuing health over damage reduction, since the latter is effective for 90% or more of the game combat

- I almost never use Quen, I just don't like it.

These of course are all points of personal choice.