If I have {Batterskull} and {Humility} in play, will it make it 5/5 lifelink vigilance creature?
Depends on what entered first.
From this gatherer ruling I think you get the 5/5. Batterskull falls into the (c) category, and humility into the (b). With that, look at the part I bolded.
10/1/2009 You apply power/toughness changing effects in a series of sublayers in the following order: (a) effects from characteristic-defining abilities; (b) effects that set power and/or toughness to a specific number or value; (c) effects that modify power and/or toughness but don't set power and/or toughness to a specific number or value; (d) changes from counters; (e) effects that switch a creature's power and toughness. This card's effect is always applied in (b), which means that effects applied in sublayer (c), (d), or (e) will not be overwritten; they will be applied to the new value.
Since I run an enchantment deck, I'll put in my idea. This is a lot like if you have {Gigantiform} on a creature with another enchantment. It becomes an 8/8 base p/t but is then modified by other enchantments. Say I have {Rancor}, it would become a 10/8.
The rule E.Kann gave is the correct one. Because of the way the sublayers work, you apply effects that set power and toughness first, then add any other things to it.
As for the abilities, though... If the Batterskull was equipped to a creature when Humility entered the battlefield, the creature will be a 5/5 with no abilities. Both Batterskull's ability-granting and Humility's ability-taking effects apply in the same layer, so the newest timestamp one wins. BUT, if you're able to re-equip the Batterskull to a creature, it creates a new timestamp that wins out over the Humility, granting the Lifelink and Vigilance.