Just wanted to summarize and break down the crossbow expert feat.
Crossbow Expert
Thanks to extensive practice with the crossbow, you gain the following benefits:
>You ignore the loading quality of crossbows with which you are proficient.
The loading property is what keeps you from attacking multiple times with a ranged weapon, simple with this feat you can now attack multiple times in one turn using a crossbow you are proficient in.
>Being within 5 feet of a hostile creature doesn't impose disadvantage on your ranged attack rolls.
Simple, this lets you ignore disadvantage for being adjacent to enemies when making ranged attacks, any ranged attack including ranged spells, thrown weapons, any ranged attack.
>When you use the Attack action and attack with a one-handed weapon, you can use a bonus action to attack with a loaded hand crossbow you are holding.
This is the one that seems to be causing debate. When you take the attack action with any one-handed weapon (this can be a long sword, an unarmed strike, a javelin, another hand crossbow, or even the same hand crossbow you are about to use) you get to make an attack with a hand crossbow you are holding as a bonus action. Simple, no talk about two weapon fighting (which only deals with melee weapons attacks).
Much like the polearm master feat, crossbow master gives you a bonus action attack. Much like that feat you add you ability modifier to the damage dealt, because nothing ever says you do not do so. The only time in the entire rules of 5e you do not add your ability modifier to a damage roll is under two weapon fighting, which is limited to melee weapons.
You can fire and reload the hand crossbow multiple times using just a single hand because the rules don't talk about needing to use two hands anywhere. The weapon does not have the two handed property, the loading property doesn't mention anything about needing a free hand, the ammunition property talks about drawing ammunition is a part of the attack not a separate action.
I hope this clears things up a bit.