This has all been very interesting reading. I have an A+ Certification and worked commercially for eight years on pc's in both software and hardware building and configuration. I still say that if you are going to make money, it's in repair. The amount of money a person can WASTE trying to over-tweek a machine won't do the tech or the customer any good. Best to go with the tried and true. Experimenting is great but best do it on your own time.

RAM is usually upgraded in pairs simply because that's what the particular motherboard configuration requires (and the bus).

Storage is wonderful but remember: The bigger the bytes, the harder the data falls when the drive fails. Best to store in multiple sources. Terabytes are terrific if you back up at least once a week. Cuz, losing all that in one failure can break your heart. Storing a terabyte in three or four separate storage sources, less room for total loss. Or use raid formation and stripe or mirror it.

2GB is plenty for games but your processor and bus must support it.

Sorry, this old brain is running out of anything further useful.