When it comes to memory, I recommend new builders use the memory compatibility list the motherboard manufacturer releases. Most memory will just work, but the compatibility list will remove all doubt and help ensure you are able to get memory that performs to spec in your setup. How much memory you need will depend upon your use, but I personally recommend 32GB if you can, especially if you have integrated graphics and you work with sample libraries. Most everything will work well enough on 16GB, of course. 8GB can be stretching it and will be limiting, but folks still use it with the limitations in mind. I have 64GB in my PC not because I use that much with a DAW, but because some of the other work I do on this PC really benefits from the additional memory.