A: Yes, it uses standard 288-Pin DDR4 SDRAM DDR4 2400. You'll have one free slot for upgrade (i.e. you may save money by buying 4GB only module, to make total 8GB - enough for home customer today).
Q: Is the Windows 10 OS 32-bit or 64-bit? If 64-bit, can the RAM be upgraded if needed later?
A: This system uses Windows 10 Home 64-bit as it's operating system. The RAM can be upgraded to up to 16GB on this model.
A: Yes, there are no built in speakers within this system.
A: No, there are no open bays for either another hard drive or another optical drive. This is a slim line configuration.
A: The mouse and keyboard are also included.
Q: Maximum Support HDD Capacity ?
A: The maximum RAM is 16GB and the maximum SSD memory is 258.
A: Mine came with a 1TB HDD, but unsure about upgrading. I am also running about 3 WD 1TB external HDD, a WD 2TB external HDD, and a WD 4TB external HDD along with numerous thumb drives, and it hasn't slowed it down. I know this does not answer your question, but hope it helps in other areas.