The Continuum 101 by Mac

Equipping bows, or any weapon, is pretty cut and dry. You need to spend an extra ability point for each rarity of bow. A common (level 1-white) bow costs 1 AP, whereas, a heroic (level 4-purple) costs 4 AP. You'll notice when you get to level 3, rare (blue) bows, that "+25 AF if using basic attack" gets added to the description. This is a passive ability that triggers automatically when you use your basic attack. Many action abilities are dependant on your basic attack so the AF bonus will apply. The abilities that say "In addition to basic attack..." are obviously the ones which fall into this category. Abilities like Leech Life and Aura don't count bonus AF into the equation, just your basic core stats.

For a little extra AF boost, multiple weapons can be equipped and the bonuses do indeed stack. It you were to equip your Ancient Bonded with Bows 3 AND Projectiles 3, he would then get a +50 AF bonus each time he used basic attack. Level 5 of weapon abilities grant a +5 DAM to your basic attack. This bonus is also stackable.

There are a handful of units which get the ability Weapon Mastery. This allows the unit to equip any weapon in the game!

Bows 1	Air Manifested - Lvl 5
equip level 1 bows	Ancient Bonded - Lvl 1
	Crimson Elf Stalker - Lvl 1
	Elfin Sentinel - Lvl 3
	Fire Bantam - Lvl 5
	Fire Manifested - Lvl 1
	Legion Archer - Lvl 1
	Legion Crossbowman - Lvl 1
	Legion Squire - Lvl 5
	Legion Spy - Lvl 4
	Lightbringer - Lvl 1
	Order Healer - Lvl 4
	Order Ranged Expert - Lvl 1
	Order Telepath - Lvl 4
	Radiant - Lvl 5
	Talon Scout - Lvl 5
	Water Bantam - Lvl 1

Bows 2	Air Manifested - Lvl 7
equip level 2 bows	Ancient Bonded - Lvl 3
	Crimson Elf Stalker - Lvl 2
	Elfin Sentinel - Lvl 5
	Fire Bantam - Lvl 7
	Fire Manifested - Lvl 3
	Legion Archer - Lvl 2
	Legion Crossbowman - Lvl 3
	Legion Squire - Lvl 7
	Legion Spy - Lvl 6
	Lightbringer - Lvl 3
	Order Healer - Lvl 6
	Order Ranged Expert - Lvl 2
	Order Telepath - Lvl 6
	Radiant - Lvl 7
	Talon Scout - Lvl 7

Bows 3	Air Manifested - Lvl 9
equip level 3 bows, +25 AF w/ basic attack	Ancient Bonded - Lvl 5
	Crimson Elf Stalker - Lvl 3
	Elfin Sentinel - Lvl 7
	Fire Bantam - Lvl 9
	Fire Manifested - Lvl 5
	Legion Archer - Lvl 3
	Legion Crossbowman - Lvl 5
	Legion Squire - Lvl 9
	Legion Spy - Lvl 8
	Lightbringer - Lvl 5
	Order Healer - Lvl 8
	Order Ranged Expert - Lvl 3
	Order Telepath - Lvl 8
	Radiant - Lvl 9
	Talon Scout - Lvl 9

Bows 4	Air Manifested - Lvl 11
equip level 4 bows, +30 AF w/ basic attack	Ancient Bonded - Lvl 7
	Crimson Elf Stalker - Lvl 4
	Elfin Sentinel - Lvl 9
	Fire Bantam - Lvl 11
	Fire Manifested - Lvl 7
	Legion Archer - Lvl 4
	Legion Crossbowman - Lvl 7
	Legion Squire - Lvl 11
	Legion Spy - Lvl 10
	Lightbringer - Lvl 7
	Order Healer - Lvl 10
	Order Ranged Expert - Lvl 4
	Order Telepath - Lvl 10
	Radiant - Lvl 11
	Talon Scout - Lvl 11

Bows 5	Air Manifested - Lvl 13
equip level 5 bows, +35 AF & +5 DAM w/ basic attack	Ancient Bonded - Lvl 9
	Crimson Elf Stalker - Lvl 5
	Elfin Sentinel - Lvl 11
	Fire Bantam - Lvl 13
	Legion Archer - Lvl 6
	Legion Crossbowman - Lvl 9
	Legion Spy - Lvl 12
	Lightbringer - Lvl 9
	Order Healer - Lvl 12
	Order Ranged Expert - Lvl 5
	Order Telepath - Lvl 12
	Radiant - Lvl 13