I'm a little iffy on some of the answers above, so here are my thoughts as an Ork player
1. How does 40K currently scale? I don't have the time for huge armies right now, so am wondering if it plays well at lower points, or if there are any rules for smaller warband/squad level combat.
7th Edition army comp is a pile of stinky, rancid fish being thrown onto a dumpster fire, but if you make up your own reasonable army comp or steal someone else's you can have fun and interesting games at lower points level. I'm not a fan of
GW Kill team, because the army comp isn't great, and the balance is terrible. Heralds of Ruin a Fan-made kill team ruleset is far better, but I'm not huge on kill team as a format.
What I really like is Combat Patrol. 400 points. 1-3 troops. 0-1 everything else except no LOW. No combined armor value greater than 33 (front + Side + Rear). No model with more than 3 wounds. No 2+ armor or invuls, and no more than 3 mastery levels. It's a fun game, and has interesting matchups for about every army.
1500 points, single
CAD still works so long as you keep out super heavies.
2. After doing some research, apparently Nazdreg ug Urdgrub isn't in the current army list - is that true? I usually don't use special characters, but I want to make a small army based upon him.
He's Gone along with a number of other Ork players, and lots of Ork options.
3. If Nazdreg doesn't exist, how could I best replicate him? It appears that kombi-weapons still exist; what is considered the shootiest of them?
You probably want Badrukk. He doesn't have mega armor but he does shoot plasma. Kombi-weapons are kinda a mess right now. The only kombi that makes sense is a kombi-skorcha. If you really want a shooty Mega-armor character, you can look at a
MA Big Mek with a Teleporta blaster. The Killdakka from the Waaagh ghazgul suppliment might appeal to you, but it is stupidly hard to take Ghaz relics these day in legal army lists, and usually not worth the trouble.
4. Is it possible to have an army of Meganobz, or at least a lot of them? What is the best equipment for them?
It is. 15 meganobz is a legal army thanks to Ghazghul's bully boyz formation. It's a minimum of 600 points, but you can easily add upgrades to it to get it around 1,000 points. In smaller games it isn't a very fun army to play against, and isn't likely to have very many close games. You'll either walk all over someone, or get demolished. I probably wouldn't look at it in games smaller than 1850 points.
I like Meganobz, but sprinkle them into my army. My favorite way to run them is 3
MANZ in a Trukk. I give the Trukk a Ram, I give the Boss Nob Killsaws and a bosepole. I give one of the other's a Kombi-Skorcha. It's a
MANZ-Missile. It works quite well in games. I usually have 1
MANZ Missile in a 1500 point army. At 2,000 points I do double
CAD, and either triple
MANZ missile or drop them from the list in favor of Tankbustas. I don't use
MANZ in games smaller than 1,000 because of the rock paper scissors nature of them.
The Current edition Ork codex along with the overall shift in the game towards psychic deathstars and high volume of fire high strength shooting has left Orks feeling fairly limited. Trukk rush can work. Bikers can work. If you are willing to exploit a clear typo, then Buzzgob's Big Mek Stompa works. If you are willing to play out of a book that is now outdated greentide works. But Orks don't have a very wide range of viable units / wargear or army builds.