At least with swords the expertise skill eventually drops your recuperation time down to zero, anyway, so the minor differences between swords become irrelevant. I don't know if that is the case with bows; level 5 Bow Expertise drops recuperation by 15, while Crossbow Expertise drops it by 5. You can also get a Speed bonus on weapons, which also reduces the recuperation time (though the net value can not get less than zero).
I believe that all bows have a maximum recuperation of 15, so maxing out Bow Mastery drops that down to zero.
A bow is a good default weapon for a mage. I chose a dagger and one-handed sword myself so I could have a shield (which meant more magical enchantments).
The best bow in the game requires 15 strength and 30 agility, so you might want to invest at least that much so that you can equip it. Don't worry, there are TONS of stat points, at the end I had 30 Agility, 70 strength, 25 Constitution and like 177 into Intelligence.