1. there are no differences in SSD for desktops and notebooks
2. Yes SSD in the 2.5 x 9.5 or 9 or 7 will all fit in your notebook no cables are needed. Look in your manual and you find direction on how to change out a hard drive
Asus Support Downloads digital copy will be found there.
3.Samsung is the best either EVO or PRO 256GB is a good size for you OS and important software. If you don't have a 2nd drive it would be good to put one in like a 1 TB 7200 rpm spinner for your less used software and data files.
4. Check Amazon and Newegg Tiger direct Fry's for the best prices One of them usually has a sale going on.
Here is another link that will be helpful for you installing window 8.1 or 7 or 10, I don't recommend ten to start with as is can be difficult to find working driver for 10. 7 8 and 8.1 have drivers on the download site I linkd you too.
http://rog.asus.com/forum/showthread.php?76993-Guide-How-to-install-windows-8-8-1-10-The-proper-way-..., That link is on the G752 sub forum but should show you the way to clean install UEFI. I recommend that you install 8.1 you may need these Generic Keys to get the install started Windows 8.1 Single Language Y9NXP-XT8MV-PT9TG-97CT3-9D6TC
Windows 8.1 Core 334NH-RXG76-64THK-C7CKG-D3VPT
Windows 8.1 Pro XHQ8N-C3MCJ-RQXB6-WCHYG-C9WKB
If you want to install
window 7 this link will show you how to install 7 UEFI
here is a
Thread in the G75 VW and G75 VX on upgrading and downgrading lots of specific information on the G75
Download
8.1 install media or ISO from MicrosoftDownload
window 7 install media or ISODownload
window 10 install media or ISO hereHope all this helps
G752VY-DH72 Win 10 Pro
512 GB M.2 Samsung 960 Pro
1 TB Samsung 850 pro 2.5 format
980m GTX 4 GB
32GB DDR 4 Standard RAM
Z97 PRO WiFi I7 4790K
Windows 10 Pro
Z97 -A
Windows 10 Pro