GoKawiilThis is super subjective. The amount of speakers you 'need' really boils down to how big your lounge is, the size of your budget and the type of content you watch. If you're constantly watching big-budget action movies, you'll likely want either a 5.1 or 7.1 system. The former normally starts around the $500 mark, while the cheapest 7.1 arrangements usually cost a minimum of $1,500. Should you really want to push the AV boat out, you could easily spend upwards of $3,000 on a 5.1 system and over $4,000 on a 7.1 setup.
It's important to note that space plays a major factor in what type of surround sound system you should go for. If you live in a cramped apartment and don't have the space for a bunch of speakers — not to mention speaker stands — you'd be better off with a quality soundbar to boost your TV audio paired with a subwoofer. Conversely, if you live in a mansion with a living room the size of an aircraft hanger and money is no issue, by all means treat yourself to a luxurious 7.1.2 Dolby Atmos home theater setup.
You can actually put together an excellent surround sound system with minimal speakers. Many soundbars now offer convincing spatial audio, like the Atmos-compatible Sonos Arc Ultra. With 14 drivers spread out in a 9.1.4 channel configuration, the $1,000 Arc Ultra can deliver a room-filling soundscape without the need for additional surround speakers. That said, if you've just won the Powerball, you can up the audio ante by pairing it with a Sonos Sub or a pair of Sonos Era 300 smart speakers for an extra $960. The likes of the $1,600 Samsung Q-Series HW-Q990F is a brilliant alternative, consisting of a Dolby Atmos soundbar, a subwoofer and two rear speakers.