Legendary.
They each have their perks. MW3 has the multiplayer playibility, but lacks a good, long story. While Skyrim has one of the best stories but does not have multiplayer. I bought Skyrim four days ago and haven't touched MW3 since
There are 13 perks in total.
If you mean the Werewolf and Vampire perks, these are not earned the same way as regular ones. As a Werewolf, progress towards new perks is earned by eating the hearts of slain victims. As a vampire, progress is earned by killing enemies with your claws or life drain power. So even if you started Dawnguard as Lv81 with all perk points spent, you can still max out both the Vampire and Werewolf perks. Dawnguard adds no other perks, so a Lv81 won't miss anything out in that regard either.
No. Perks are only ever granted on level up, and there is no shortcut to get the better perks apart from training the skills to the prerequisite level.
When you switch to a vampirelord, you can check what perks you have by pressing B, like you were trying to get to the menu. Normal vampires don't have levels or perks.
I would advise that you start off as a dragon. The dragon has the best perks.
You have to have one of the perks that allow you to do it. If you have the perk, draw your arrow, then hold the secondary weapon button.
Dawnguard is the expansion that adds the werewolf perk tree, without that, you can't get werewolf perks.
Some do, some don't. Augment Flames will affect Flame Breath, for example, but Intense Flames does not.
You have to buy specific perks on the One-Handed or Two-Handed skill trees, or the Sneak tree for backstab criticals.
81 because that is the highest level and you only get 1 perk point per level
Vigilants of Stendarr wear regular novice robes (self-enchanted or college robes), a hood, steel gauntlets, steel boots, and an amulet of Stendarr. They level up mostly in Restoration, with a touch of Alteration skills. Their inventory may include a torch, a low level knife (iron-steel-elven-dwarven), and one of the following books: The Book of the Daedra, Immortal Blood, Physicalities of Werewolves. They are extremely anti-Daedra, so if you want to be a die-hard-vigilant, then don't do any quests that involve siding with Daedra