WIP: My adventures with 2011 MacBook Pro and Windows 8.1 including seconday HDD

Question

So I've just lost about 3 days of my life trying to install Windows 8.1 (my preferred) operating system on a Late 2011 MacBook Pro.
I feel that I've learnt a lot and hopefully can share my experiences to speed a few of you along the process. This is my own experience please let me know if anything I have documented is not true and I will revise for completeness
What my initial goal was to have a dual HD set up with an SSD running both Mac OSX and Windows 8.1 (via Bootcamp) with a 2ndry HD in places of the optical (DVD) drive for shared storage.
I have tried all/some of the following:
Win 8.1 ISO from the MS site: http://windows.microsoft.com/en-GB/windows-8/create-reset-refresh-media
USB created using Rufus for Bios and EFI boot
DVD created using Windows 8.1 (can't remember how)
Yosemite USB created using: Create a bootable installer for OS X Mavericks or Yosemite - Apple Support
There are 2 main options when installing Windows:
Bios
EFI
Both have different pros and cons, which Im going to try and document here:
Bios
Full driver support via Bootcamp download
Slower (mainly boot time, not by much though)
Not quite as "native" as some may prefer
Limited number of partitions??
EFI
Fast
Native
Does not support video driver properly (no dual screen)
Audio does not work (says Failed to start device)
Here are some random facts I know
Windows DVD will only boot from optical drive when connected internally. If plugged in via external USB it stops at black screen with flashing cursor and doesnt progress
Using 5HT-2a's method on Redit (see below) and the EFI install, I get the Cx0000005 cannot find source media error and cannot install
Hacking the Bootcamp tool to create a Windows 8 ISO with all the drivers works (see link below) but when using it in EFI it crashes repeatedly during install so you never can complete the process (I think this is due to the video drivers) and therefore can't run Bootcamp assistant thus get proper trackpad support
Using lion10's method (below) for tweaking a standard Mac partitioned HD I was able to get past the cannot install Windows error ("windows cannot be installed to this disk. the selected disk is of the GPT partition style") and install Windows using EFI
Best guides/links I have found:
lion10's method:The ultimate way to install Windows 8.x in (U)EFI mode on Apple systems
5HT-2a's method: http://www.reddit.com/r/mac/comments/2fy3be/by_popular_demand_my_better_than_boo tcamp_guide/
skipsizemore's method: Can't install Windows 8 x64 on late 2013 MBP with1TB SSD
Bootcamp drivers 2 versions depending on Mac:
Older Macs: Boot Camp Support Software 5.1.5621
Newer Macs (most 2013+): Boot Camp Support Software 5.1.5640
Bootcamp Assistant Hack for USB creation on older Macs: http://forums.macrumors.com/showthread.php?t=1680652There is an additional parameter required if you are using Yosemite during code signing (-deep I think, but cant remember)

Answer 1

What I ended up doing (so far)
I'm not 100% sure of the state of my disk when I got to where I ended up but I had previous completed the GDisk and DISKPART methods from 5HT-2a and lion10's methods. I was using a 128gb SSD
I then decided to start from the top (as I had previous installed Win 8.1 on the original HD using DVD)
So I ran the Yosemite installer (via USB) and used the partition tab in Disk Utility to repartition the disk into 2 partitions, 1 for OSX and 1 (ExFat/NTFS) for Windows
I then booted in Bios (Windows, not EFI) using the Windows 8.1 DVD using the DVD plugged in internally (wouldnt work using USB enclosure)
Installed Windows to the partition I created (probably the 4th one)
After Windows installed, ran the Bootcamp set up program
Reran Yosemite installer and installed Yosemite
Swapped out the optical drive for a larger HD (7200rpm) and formatted it with HFS+