Forget Pcie. You only have one which your gpu will use.
you have 4sata which can connect to 4 2.5in ssd or 3.5in hdd up to you.

you have one m.2 slot (under the silver plate with the aorus marking)
you can slot in either:
m.2 ssd (500 speed) or
m.2 nvme (3500-1800 speed)

nvme>ssd>hdd
(3500-1800)>500>150(i think) speeds

C drive should at min ssd

recommended nvme
samsung 870 evo plus (almost best of the best)
adata xpg 8200pro (fast value for money)

recomended ssd
2.5in crucial mx500

nvme to ssd for game loading maybe faster 7secs so you wont really feel it.
If your app read write a lot like video editing then you will appreciate the extra speed.