You do not need to put anything into health or stamina if you play as a mage. I haven't played Dawnguard, but vanilla Skyrim on master can easily be done with 100 health.
I recommend not taking this approach, change phrase to "can easily be done with reloading everytime something unexpected happens" and that will be more accurate.
Maybe its just me- i hate dying, and 100 health pretty much garantees that will happen, even if you are super careful, and if you arent- it will happen quite often.
Skimp stamina? Sure- but not so much on the health.