Question about Gigabyte B450M DS3H

Anything that actually works. Based on the price, a RAM kit with 2x 16 GBite sticks at 3'200 MHz could fit. You can also use either a SATA SSD or an M.2 SSD (with SATA protocol or NVME protocol).
You can also use any graphics card you like. They are all equipped with the PCI-E x16 standard.

Unfortunately, I cannot make any direct product recommendations with the information given. For that, I would have to know what the PC will be used for, what the requirements are and how much money you want to spend on it.