Gladius Legis
Legend
There is obviously some disconnect here.
1. You move into melee range with an enemy.
2. You use the Attack Action to attack it with your Rapier (everyone loves rapiers).
3. Hooray! You made a melee attack! Now your enemy loses AoO against you for the rest of your turn thanks to Fancy Footwork.
4. If you want to, move away from the big scary enemy.
5. Attack something with your hand crossbow.
6. If you didn't move before shooting your hand crossbow, now take the opportunity to move away from the big scary enemy, still with no fear of AoO thanks to Fancy Footwork.
7. Profit.
You're going to run into some tricky logistics if you try that, considering you still need a free hand to load the hand crossbow. (Equipment, p. 146 in errata.) You'll be stowing and drawing your rapier a lot, which means you won't be able to do this every round.
Assuming your crossbow is loaded at the beginning of your first round, you'd be OK. But your second round would then go:
1) Rapier attack
2) Stow rapier (free object interaction)
3) Crossbow attack
You can't draw your rapier again until the third round, since you already used up your one free item interaction in the second round. Your third round would then go:
1) Draw rapier (free object interaction)
2) Rapier attack
3) No crossbow attack for you, since your hand is full and you can't stow your rapier since you already drew it this round.
Round 4 onward would repeat what happens in Rounds 2 and 3, which means you'd only get your extra crossbow attack every other round.