Get Ultimate Apocalypse mod. It adds 3 new races (Tyranids, Chaos Demons and Inquisition), a ton of new buildings, units and ability to level up commanders. The mod tends to crash when trying to play 8 player scenarios, and you're going to lose a lot of fps during bigger battles since the engine is outdated af.
There are a lot of people playing, just check out mod's Discord server and ask if anyone's up for a match (there's also patch for newest version that balances most broken stuff). Devs are very chill and actually listen to feedback.