Fighting Style is Two Weapon Fighting. Mastery in dagger(Nick) and shortsword(Vex)

Using Hunter's Mark and, I hope, Colossus Slayer. DEX is 17 (+3)

My question is what happens if I want to develop dagger throwing for opponents beyond 5 feet? What die to use for "hit" and "damage"? I assume it's still piercing damage. Does HM apply? Nick? CS? Vex?

On my next turn, can I pull another dagger out of my armor and use it? Would I be better playing two daggers and throwing from either hand?

This is my first DND character, so please forgive me if what I'm saying makes zero sense!

Throwing the dagger will generally work the same as using it in melee. It’s a finesse weapon, so you can use dex instead of str. Weapon masteries of the dagger, hunter’s mark and colossus slayer will all work as normal. It will use the same damage die.
One thing to keep in mind is a dagger’s range which is 20/60. Attacks within 20 feet are as normal. Between 20 and 60 feet, you’ll have disadvantage since you’ll be at long range. And you can’t throw it at something more than 60’ away. Well, you could technically try and throw it, but beyond 60’ you just miss.

The only thing that won’t apply is vex, as that is attached to your short sword, so it won’t impact attacks with your dagger.

Everything Xalthu said here is correct, but just to address your last question: you can generally draw one weapon as part of making an attack with it, so you don't necessarily need to keep two daggers out all the time. Using the shortsword in the other hand instead may be a better choice for two reasons:

1. If you get into a melee fight, you may appreciate the slightly higher damage output of the shortsword.
2. The shortsword's Vex property will help you get advantage on subsequent attacks, whereas having two weapons with Nick has no benefit over just one weapon with Nick.

Thank you for your replies.

Let's say I had cast Hunters Mark on a previous  turn. On this turn, I strike my "prey" with shortsword and kill it using 1d6+3 from shortsword and 1d6 from Hunter's Mark. I decide which opponent to strike next, use my Bonus Action to redirect HM to it, and attack it with my dagger doing 1d4+3 and 1d6. I don't get to apply vex (Advantage) from the shortsword because it only works for attacks against the same creature. Assuming my new target is below max HP, I use Colossus Slayer to do an additional 1d8 damage.

But, maybe not. Does the new target have to be below max HP before I use the dagger? Or can I use Colossus if my dagger was its first damage?

Thanks!

Quote from Nosy_Gnome >>

Thank you for your replies.

Let's say I had cast Hunters Mark on a previous  turn. On this turn, I strike my "prey" with shortsword and kill it using 1d6+3 from shortsword and 1d6 from Hunter's Mark. I decide which opponent to strike next, use my Bonus Action to redirect HM to it, and attack it with my dagger doing 1d4+3 and 1d6. I don't get to apply vex (Advantage) from the shortsword because it only works for attacks against the same creature. Assuming my new target is below max HP, I use Colossus Slayer to do an additional 1d8 damage.

But, maybe not. Does the new target have to be below max HP before I use the dagger? Or can I use Colossus if my dagger was its first damage?

Thanks!

I'm pretty sure the intent of Colossus Slayer is that it only applies if the creature were missing HP before the attack you're using Colossus Slayer on. Otherwise it would just apply to every attack.

You might want to look into Sharpshooter so you can ignore cover and long range.