So, 'Soul Land' got me so hooked I started hunting down everything Tang Jia San Shao wrote, and the reading order gets messy fast because of the web novel serialization and the multiple storylines. The main series, the original 'Soul Land', is definitely where you start. It's Tang San's journey, and everything else builds from that. After finishing it, I'd say jump into 'Soul Land II: The Unrivaled Tang Sect', which continues the legacy but with a new protagonist. It feels like a natural progression of the world.
Where it gets tricky is with 'Soul Land III: The Legend of the Dragon King' and 'Soul Land IV: Ultimate Fighting'. They're set further in the future, and while you could read them after II, there's a huge time jump. Personally, I read III and IV later and didn't feel lost, but the tone shifts a lot. The prequel, 'Soul Land V: Rebirth of Tang San', is a recent one. It's actually a prequel to the original, exploring Tang San's life before the events of the first book. I'd save that for after you're already invested in the character, because its impact relies on knowing who he becomes. The spin-offs like 'The Legend of the Divine Realm' and 'The Skyfire Avenue' are connected in the broader 'Soul Land' universe but are more like side stories you can explore if you're still craving more after the main sequence.