Depends on budget but for current gen stuff I'd go for ryzen 5700G 8 core processor with built in graphic.. Still go b550 board, 1tb m. 2 storage, 16gb 3600ram. Then get a capture card.
Then in the future if you want to game on the pc, you can just drop a dedicated gpu in.
If you want to go cheaper 3600 cpu with b450 board, still 16gb ram and m. 2 drive, with capture card.. Youd need a cheap gpu to slot in though as no on board graphics. Away at mo and dont have pc to check prices etc.
I dont do any streaming so hopefully someone else here can fill you in a bit better thsn me