Minecraft is over-saturated on YouTube, it has reached its plateau and is only going downhill from here.
Try picking up a cheap but clear mini-tripod desktop mic for $15 on amazon, throw a sock over it as a pop filter and call it good.
Play some less hardware demanding games. There's plenty of 2D games out there people might enjoy watching. An easy starting target would be Terraria.
If you still insist on 3D gaming on your old computer, look for games from before 2010 that run on DirectX 8. Portal 1 might be alright. People still love Half-Life 1, people would watch that for sure and I guarantee you can run it.