Well you can just have the 256Gb SSD for booting and the HDD for storage, each one 1 partition. I dont think they send it parted in 2 halves 😄

Yes the partitions are so that you keep your OS partition small and easy or image and restore should problems arise.
Download Asus Backtracker and create an restore media This is the very first thing you should do!!!

You should thoroughly test out your new NB use any Benchmark testing program you can get or borrow you'll want to force you CPU to Run at 100% for at least 15 minutes Temps shouldn't get much over 80C I use Burn in Test
You can use Furmark to Stress test your GPU a full run of 15 minutes at full screen 1080 again your GPU shouldn't get much over 80C

Hwinfo64 will show you your loads temps and fan speeds and just about everything else about your notebook including driver versions RAM Timings and voltages.

Make a point of testing every system of your new notebook. WiFi, LAN, Audio, USB 3.0 track pad everything. If all is good then install your software and games on the 😧 part of your SSD, start having fun with your new notebook.

Failure to test and back up could cause you a lot of stress later on.

You can partition your SSD and Hard drive any way you want. I have my SSD C: = 256gB and my 750GB = 😧 where I have most of my programs installed and E: where I have my Data I use Mini Tool partition wizard and recommend it for UEFI systems