HP Proliant DL580 g7 - Adding Hard Disks and Graphic card

[OwickedG]

Good day All,

Not so long ago i bought a G7 server to be used as a homelab.

Not knowing many about server builds (I do about regular) I have a need to expand my storage place on the server.
While in the front of the server i already am using one SSD disk i want now to add a mechanical with more capacity.

Unfourtinetly i bought a new disk with the size of 3.5 inch and it will not fit in the front as it seems to only hold 2.5 inch, So i assumed i can add the disk internally, after looking arround my options are quite limited.

I did find a connector for SSD's wich seems to also fit the hard drive (same picture as below), As it is a mechanical hard drive i dont think having it stand up is a smart move. My question is if there should be a other place with a sata connection or can i buy some kind of extension coard for this connector and place the drive somewhere safe?
https://www.servershop24.de/item/images/114880/1280x1280/114880-2.jpg

And the extension cable i am looking at:
https://images-na.ssl-images-amazon.com/images/I/51EGCOvja0L._SY355_.jpg

My second challenge is adding a graphic card, the card i have requires a 6 pin cable, I understand that all my power supplies(4 are connected) connect to a power board and the power is distributed from there? 

On that board only 1 of the 4 connectors are connected, After googling i found a cable exist from 10 pin to 6 pin. Could i power this way the graphic card?

The Power board:
https://images-na.ssl-images-amazon.com/images/I/41Iouwu6gOL._SX355_.jpg

Cable i am currently looking at:
https://www.dhresource.com/0x0s/f2-albu-g5-M01-94-55-rBVaJFhUKCuAdpYxAARxbOI-HM8817.jpg/psu-10pin-to...

Would apreciate any kind of advice and my excuses if i missed the right topic on the search and google, could not find a trustworthy answer.

With kind regards,
R