You would need 100 in all skills and 89 in one, so 1484 skill levels ([100 - 25] + 5 * [100 - 20] + 12 * [100 - 15] - [100 - 89]
).
What's that, you want an explanation?
The formula to level up is:
XP required to level up your character = Current level * 25 + 75
if you remember your math classes and that whole sum(1..n) = (n + 1) * n / 2
business, that means we need
(81 * 80 / 2) * 25 + 75 * 80 = 87,000
skill ranks to level 80 times (from 1 to 81). We start off with one skill at 25, five at 20 and the rest at 15. Leveling each skill to 100 gives us
(100 + starting level + 1) * (100 - starting level) / 2
points, which brings us to 4725, 4840 and 4930 skill levels, respectively. If you level up all skills except one fully, we're at 83155 (4930 * 11 + 4840 * 5 + 4725
), so still 3845 skill levels short. So with that last skill, we can solve for the the final level required:
(x + 15 + 1) * (x - 15) / 2 = 3845
(x + 16) * (x - 15) = 7690
x^2 + x - 240 = 7690
x^2 + x - 7930 = 0
x = [-1 + sqrt(1 - 4 * -7930)] / 2
x = (178.10 - 1) / 2 = 88.6
x rounds up to 89
Note:
Using a major or minor skill here wouldn't affect the calculation:
(x + 25 + 1) * (x - 25) / 2 = 87000 - (4930 * 12 + 4840 * 5 + 4725 * 0)
(x + 20 + 1) * (x - 20) / 2 = 87000 - (4930 * 12 + 4840 * 4 + 4725 * 1)
(x + 15 + 1) * (x - 15) / 2 = 87000 - (4930 * 11 + 4840 * 5 + 4725 * 1)
Also, you can test it out with an online character creator, like this half-baked one I threw together.
Edit:
Semi-interestingly, if you want to know the maximum number of levels required, it's only one more than the minimum. It would involve 8 skills at 100 and 10 skills at 99, so 10 less than the maximum number of skill increases available versus 11.
Edit 2:
In case anyone's confused about why I'm ignoring major/minor skills or anything else that might have affected a character in Morrowind/Oblivion, there's a great answer on this topic. All skills are born equal. Leveling a major skill Sneak from 30 to 31 is the same as leveling a standard skill Sneak from 30 to 31, which is the same as leveling a minor skill Archery from 30 to 31. All of them give you 31 points of "skill level XP" or whatever we want to call it. The bottom line is that these mechanics are understood and the above answer should be true for all races and all skills.
Yes, you can still join them as a werewolf.
The Dawnguard, as an organization, are completely dedicated to hunting down vampires. Being a werewolf doesn't matter to them in the slightest. As long as you're not a vampire, they're okay with you joining up.
You will, of course, need to not have joined up with the Volkihar Clan in the Bloodline quest. If you've outright sided with their enemies, they're not very forgiving, and will still consider you the vampires' ally, even if you get yourself cured of vampirism.
Best Answer
Much a like the 'Dismay' shout and the Nord power (which i never used) the 'Howl of Terror' will have an effect throughout every level in the game.
Note that that the spell tome which also has this effect will later have no effect as you level up.
If you wish to boost smithing or any other skill i suggest you do this late on as your combat will be less effective throught higher levels when enemies get stronger. (DONT CHEAT) :)