most new mb the sata ports Are set to achi by default. you wont need to change them if they are. (you mb guild will tell you the default settings of the sata ports)the other option are ide (for old os and hardware and raid (where set two disk up to copy data from one to the other on the fly so you dont lose work if one drive dies.) (simple exp of raid).
I'm flipping through my MB guide and it's not saying what they're default set to unless you're referring to the BIOS setting as it's defaultly set to "native IDE".
the only thing on a new build in the bios that need to be check or changed is that the mb is running the right cpu and ram speed. most mb if set to auto from the factory will read both right. on some mb and ram you have to turn on xmp profile to get your 1600 or faster ram to run.
I think everything involving the CPU and Memory in BIOS is set to auto.
to install windows 7 set the boot order to cd-rom/hard drive and put the windows 7 cd in the cd-rom drive. when you power up and the cd-rom reads the windows cd it say "hit any keep to boot from cd-rom). hit the any key to boot into the windows 7 cd. windows 7 will ask for the oem number then it read the hard drive info. if there no partion all you have to do is hit enter and windows 7 will make 2 new partion for you the system partion and the data partion. if there a partion on the hard drive you have to go into advance mode and delete it and then reboot. once windows 7 installs itself and reboots dot hit the any key on reboot (on the second reboot windows 7 will install itself).
I'm currently trying to boot windows 7 from a USB via a ISO I got from mydigitallife.info and used the windows 7 USB/DVD download tool. Whenever I restart my PC, I hit f12 to select to boot from my USB flashdrive, the windows 7 starts, and I delete all partitions and I have the option to load drivers before I start. Now, I know I'm not in need of the raid drivers on my mobo driver/install disk but I'm not sure again if I need the AHCI drivers. I believe when I tried installing before, I used Native IDE in bios and when it installed it blue screened. Then I switched bios to AHCI, installed the AHCI drivers via the mobo disk, and the windows 7 installer got to "finishing installation" and sorta got stuck on that screen. The process is a little different in order, I was oddly enough never prompted for a OEM key or time/date as it didn't finish.
Everything else in your post isn't really applicable yet as I'm still stuck here but hopefully we can get past that haha.
Also, to Kenrivers. My motherboard is a gigabyte 990XA-UD3.