Yes, they would all proc on the first hit. A good thing to keep in mind is that Spellblade has a 2 second CD. so to get the most use out of it time out your abilities accordingly.
If youre going full AP youll probably benefit more from a combo burst. Example: Hitting an opponent with Q, E, R in rapid succession. Lux is squishy so its pretty risky to hit them with your q, then get in range for an auto attack because any half decent assassin can take Lux out once the stun wears off if shes still in range.
Lichbane is a recommended item in Dominion however because youll often be in teamfights where youll have to stick around for a while instead of hitting the opponent and then backing up to the safety of your turret.
Hope this was helpful advice and goodluck!