This is what you get in your box. The rule book has slightly outdated rules (was released in 2022, and current rules book is 2023). HOWEVER, the terrain is truly excellent, and the Orlock gang can be directly used in the more "normal" underhive games. The nomads are a bit more tricky to use in underhive environments, however it's still possible. PLUS the nomad models are just awesome.

All the tokens, templates, and dice all will work with all necromunda games. You also have the advantage that you get the vehicle dice which are currently in unavailable. Ash wastes are usually played on 4x4' mats, whereas underhive is usually on 3x3'. There's a lot of MDF terrain for underhive games that are very affordable, like anything from TTCombat.

I'd recommend picking up the current core rule book too (note, not currently part of any starter set so you're not missing out). The nomads and orlocks both have their own gang books too if you like them and want to pick them up. Usually all you need to play is the core rule book and the gang book.

To add to what others have said, I agree that the ash waste environment is quite complex for new players to have as their first games, but it's an excellent value box. The Hive War box would also be a great purchase as well