The server chassis I've just bought has a BPN-SAS2-846EL1 in it, as far as I understand it, you only need 1 SAS cable for all the drives.

I've looked through posts here and seems people say the second port is for redundancy and/or more bandwidth. I'm not as sure on that one. How about the third port though?

This is what my backplane looks like.

I've recently picked up a Supermicro CSE-846. I bought this rack and these rails.

As the rack was adjustable, I figured it was as simple as setting the rack depth to the same as the server (26") and then installing the rails. However, the rails appear to be longer than the rack. I struggled to find any helpful tutorials or installation documents for these rails and server.

Also, in the instruction manual for the SC846 (I think that's the same server?), the inner rail doesn't extend past the end of the server. Have I done something wrong?

Bonus question, the screw holes on the server and rails don't seem to fit M6 screws, are they M5? Will that still work on the rack if it came with M6 mounting screws, square nuts etc.?

Here's a couple of pictures of the rails. https://imgur.com/a/4m0DkRW