Interesting, I know it is hard to get used to a new platform, but do you mind if I try to shed some light on some of the issues you are having? maybe it will help.
I know that HD Mode does care about the type of input, like for instance a D-SUB connection between a GTX580 and a 1080P monitor wont work, but if you change it to HDMI it will work. I think maybe it needs to detect the resolution of the display, they are working on this as of now, but the thing is this UEFI is pretty big, even on a 24inch monitor b/c of its size the font is smaller than with non HD mode, so I actually like the non HD mode since the fonts are a bit bigger. Your GPU must also be supported, but they keep updating the list for older cards I am told. If you want to check if your GPU is not supported or if its your monitor, you can always use the iGPU outputs on the motherboard instead of your GPU, so unplug your GPU and then try to use one of those outputs.
With easytune crashing two things, make sure Intel ME Driver is installed(this is the management engine driver), also make sure that apart from you VGA driver and Chipset driver you also make sure no other hardware monitoring app is running. I have seen two users who said it wouldn't launch, one was fixed by installing the ME the other fixed it by closing hwmonitor.
The LED Post codes are part of the new AMI UEFI, everyone uses basically the same post codes, with A0 meaning that you are in windows and Ab means you are in the UEFI. I can help you with some others in case you want to know them, usually a hang on 15 or 51 means memory, 9A means BCLK wont go further. When you set a BCLK or a divider the system should go to 95 and then restart, when it restarts it should boot up fine. FF isn't around anymore as before GBT and others might have used AWARD BIOS, but now its only AMI as that is who Intel picked for their UEFI codes and they are much different than before. Also before you see video you should see the code 62 for GPU initialization, then you should see the BIOS screen. When in windows if you sleep or hibernate you will see either 03 or 04 after you recover from sleep or hibernation, this is normal.
QFlash requires FAT32 or FAT16 USB drives.
Classic mode will be around until they transfer all the things over the Windows mode such as BBS priorities, they are moving at a decent pace in making the Windows mode better.
The mouse sensitivity thing is being looked at, it actually differs BIOS to BIOS, I think it might be a good idea for them to put a setting in the UEFI for users to chose the sensitivity.