Galuf
is quarter of the way to immortality
Master of Kittens

How is your first day going?

Oh. :/

After the gym (especially if you lose someone), go back and grind on an earlier route for a bit, not the next one.

Also, don't forget, if you get Sand Attacked a lot, switch out to reset the accuracy.

Well, on the plus side, had you beaten him, you'd get Work Up as a TM to use yourself.

Pretty much. A lot of people comment that Nuzlockes tend to get harder as you get further in, because the last few bosses/gym leaders tend to be really powerful. But, personally, I think they are at their most difficult early on, because a single tough gym leader like Cheren with his Work Up spam, or Norman with his two Slakings in Emerald, can just absolutely wall you before you get the variety to handle them. Late game, it's just a matter of using your best team, and being willing to grind them to the point that they can stand up to the tough matches. Once you get Fly and Rods, you get a huge number of Pokemon to choose from, so, in my opinion, it gets a lot easier as you get further in.

Um, probably Black 2, just because it throws so much at you in the early game. The Work-Up spam with the first Gym Leader sucks. Most of the others start easier early on, but they get hard near the end. Black just gives you lots of grinding opportunities to take advantage of. Don't let yourself get suckered in to thinking you're okay with it.

After, Black 2, I'd say Emerald, because several of the late-game Gym Leaders suck, then Soul Silver, just because of how annoying the grind is.

Of the ones you have, I'd say the original Black. The AI in Soul Silver is a little annoying, but the big problem with it is that wild Pokemon are lower level and hard to grind against. Emerald upgraded to a couple of really tough gym leaders over Ruby/Sapphire (3rd and 4th gyms, specifically). The original Black has decent variety, you get a couple good gift Pokemon early (including a Pansage/sear/pour to super effective the first gym leader), and the gym leaders don't have tons of Pokemon. Just train hard, don't be afraid to use items, and go slowly.