You don't need two PC's to stream to be a successful streamer, but it does have 2 big advantages:
Milan 'Milan' Lopes is a well known competitive Fortnite player. He has won the 7x Epic Invitational Winner.
For gaming, Milan uses a Intel Core i9-9900KF CPU with a GIGABYTE GeForce RTX 2080 GPU. He uses a GIGABYTE Z390 Aorus Master motherboard. Milan uses G.SKILL Trident Z Neo 32GB memory and a Samsung 970 EVO 1TB SSD for storage.
For streaming, Milan uses a Intel Core i7-7740X CPU with a NVIDIA GeForce GTX 1080 Ti GPU. He uses a ASUS ROG STRIX X299-E GAMING motherboard. Milan uses CORSAIR Vengeance Lpx 16GB memory and a WD Blue 3d Nand 500GB SSD for storage.