Most people don't really know what they are talking about, but information about the GPU is correct. Minecraft is a CPU bound game, it barely even uses the GPU at all! So here is what you will be looking for.
RAM: 6GB min (I'll explain later)
CPU: Any AMD APU, if you are on a budget. The A10-5700 can run Minecraft at 90-100fps.
HDD: Anything with 7200 RPM, or SSD. (the hard drive really doesn't matter)
GPU: will be included with AMD APU (if you use intel, any cheap GPU will do)
You don't need 8 GB of RAM for Minecraft. Not in the slightest. It rarely uses over 1 GB, ever (never had it use more than 800 MB)
You are right, Minecraft doesn't use the 1GB of RAM allocated from the java heap. This does not mean that Minecraft doesn't cause your CPU to draw more RAM. RAM is essentially the quick and temporary storage for your CPU. If you have smaller amounts of it, it will take longer for the CPU to get it's stored instructions. Having more RAM doesn't actually increase FPS (unless you have a very low amount), instead it stops your game from freezing/dropping a lot of frames.
If you need more in-depth help, feel free to message me.
