Dark/Dark for a newbie

so, it's been awhile. Last time I tried a scrapper and, well, it was kind of dull. He was easy to build though. Power choices and slots were pretty standard, at least I THINK I was doing it right.

I wanted to try something different (and hopefully more interesting). I'm not exactly sure how this game works and all. I wanted to have a plan before I went in with this character, but I'm clueless where to start.
Do I end up with the majority of my primary?
Any powers that are considered useless? (like Taunt on a scrapper)
Is there a generic slotting solution?
Are there any travel powers (or other pools) that work well with Dark?

Gonna try and answer your questions in order. For general /Dark information however, I've got a guide in my sig.

Generally you want most powers from your primary since dealing damage is important.

That said, there are a few you might want to skip because they're stinkers/are situational/dependent on preference. For Dark Blast, Torrent is terrible because its a KB cone with terrible damage. Dark Pit you may or may not want. It's an AoE stun, but the numbers are pretty bad and it'll only stun minions and lts. That said, it will stack with Howling Twilight from your secondary. So my recommendation for that would be to play with it and decide if you like it. You might also want to skip Moonbeam because its a snipe, but thats another question of preference. Finally, Blackstar you might want to skip because while its a nuke, it doesn't do a lot of damage and outside of APP powers you don't have a way to regain your endurance after the crash.

Generic slotting solution would be 1-2 acc, 2-3 damage and 1-2 end rdx and/or recharge depending on the attack. This will ensure you get enough accuracy, damage and end redux/recharge as needed. If you're not going for sets though, my recommendation would be frankenslotting your powers. That's mixing and matching IOs that enhance multiple aspects of a power from different sets. For example, several acc/dam IOs from different sets. This is a much more slot efficient way to slot a power, often giving you more than 5-6 slots worth of enhancement.

Travel powers that work well for a Dark...I'd say Speed. Hasten brings up your powers faster, which is great for stuff like Tar Patch, Howling Twilight, Fearsome Stare etc. It'll also help you cycle your two damage cones (Tenebrous Tentacles and Nightfall) faster. The stealth from Superspeed will also stack with the stealth in Shadowfall granting you complete invisibility. That means you can position yourself to line up your cones without getting shot at until you start the fight.

Hope that helps

Oh and last thing, Confront/Taunt is far from useless on a Scrapper.