Attributes don't Stack, in any way. A sword with an attribute of 10 Attack Damage and sharpness doesn't change the sword any higher then 10 Attack Damage.

/give @p diamond_sword 1 0 {AttributeModifiers:[{AttributeName:"generic.attackDamage",Amount:5d,Operation:0,UUIDLeast:1l,UUIDMost:1l,Name:"testSword",Slot:"mainhand"}],ench:[{id:16,lvl:5}]}

A Full armor set designed to bring the players health down to 5 only counts for the last item you equip, or in the case of re logging only accounts for the helmets information.

An armor set that increases the players attack damage and a sword of +2 attack damage only give you +2 damage from the sword does not include the armor stats at all.

Keep in mind the +attack damage rewrites the swords damage, (I personally like it this way because a player that wants it to stack with the sword damage could just add the sword damage to the wanted attribute)