A:Answer 6 USB (2 front 4 back), 4 HDMI, DVI, 7-in-1 card reader. I haven't looked inside at slots personally.
According to HP, the board has:
One PCIe (GEN 3) x16 socket
One PCIe (GEN 3) x1 socket
One M.2 socket 1, key A
Only two RAM slots, with a max of 16 GB total.
Looks like it uses Realtek HD Audio.
The specs from HP are here: https://support.hp.com/us-en/product/omen-by-hp-870-200/13687063/model/15741160/document/c05389962