Basic Concepts for The Crystal Marksman - Champion Concept Please Comment Suggestions

First off, for some lore, I imagine it having something to do with Skarner's kind, not sure exactly what though.

He's pretty obviously by the title supposed to be an ADC.

For abilities, I have this idea for a champion who uses a crossbow - and feels like he's using a crossbow. Being a Twitch main and playing a decent amount of Vayne, I have noticed that both of the champions that I think of when I think "Crossbow" just stack a bunch of attack speed and kill things with attacks coming out at light speed - but, for a crossbow, that just isn't realistic. Crossbows are slow-firing, but penetrate through armor fairly easily in the real world. As such, my idea for his passive is that he has a very low base attack speed - something around 0.5 - with a cap at 1.5 attack speed instead of 2.5, however he gets free % armor penetration that scales with the enemy's level, similar to lethality. Also, because attack speed scales on the base, I will have to make it so that he gains bonus attack speed from items, but haven't done much with the numbers yet.

Q should also be a fairly low cooldown skillshot ability that pierces enemies killed for a small amount of bonus range on future hits and hard resets his basic attack timer - so you can basic attack, cast Q, then basic attack immediately after as if you didn't have insanely low base attack speed - again to compensate for the low base in the early game.