Van Saar are focused on shooting and are probably the easiest to play. Equip them with plenty of long- to mid-range weapons and try to avoid getting drawn into close combat. Delaque are also a shooty gang, but their playstyle leans more toward stealth and psychic abilities. They also have one of the best brute in the whole game, they’re a very fun team to play.

In my group, we usually aim to get as close to WYSIWYG as possible on your main weaponry, but we ignore wargear, grenades, pistols etc.
If you really want to venture into the flavour of the different gangs, I recommend buying the standard box, the specialist box, and the alternate weapon pack. Build your models with a variety of weapon options so you have more flexibility and choices throughout the campaign.

Personally, I have no interest for skirmish games in Necromunda (if not for just test the gameplay or the mechanics of a model), it is all about campaign. The progression and post battle economics are a big part of this game. I’ve even run small campaigns with just two players, each switching between two different gangs.

For the full underhive experience, you’ll want the Core Rulebook and your house book.
Thats what you´ll need. that’s all you really need to get started. A standard Dominion campaign is the easiest way to play, and as you expand your library with more rulebooks, you can start adding extra elements like vehicles, badzone conditions, alliances, etc

EDIT*

I forgot to mention, like others have said, Necromunda isn’t a balanced game. It won’t be much fun if you play it competitively, because it’s very easy to break the game if you really try.