I did a very similar thing but I too was installing 8.1 from a downloaded file off the Windows web store. I am running:
Macbook Pro
Retina, 13-inch, Late 2012
2.9 GHz Intel Core i7
8 GB 1600 MHz DDR3
Intel HD 4000 1024 MB
OS X 10.9.1
First things first upgrade to Maverick and get all other system upgrades.
If you are currently buying a new 8.1 OS, you can either get the install CD or a downloadable .exe install file.
I got the downloaded version b/c I do not have an optical drive.
The first thing I had to do was get on a Windows PC and run the .exe install file on a 8Gb (or larger) usb stick. This must be FAT formatted, make sure you do this ahead of time or you will waste a lot of time.
You will be asked to enter your license key, don't worry you aren't installing or binding it to the PC you are using, this is just for verification. Follow with all the steps it asks for, there will be downloads and other checks that Windows goes through, but the last step will be it asking if you would like to make a USB boot disk, or an ISO file. Choose the ISO and put it on your USB.
Next, you need to put the ISO onto you Mac b/c the USB will be formatted during the following steps.
Run bootcamp, check all three options.
You need to put your ISO and the bootcamp files on the same USB stick.
After bootcamp does its thing your computer will restart and start up windows. DO NOT START UP WINDOWS!
Hold option key and select your Mac HD.
Open Disk Utility
Select the Bootcamp partition. MAKE SURE BOOTCAMP IS THE SELECTED DRIVE!!!
Click the minus button.
Click apply.
Press the plus button to add a new partion. (automatically called MACINTOSH HD2)
Select the partion and settings will show up on the right.
Rename the partition to BOOTCAMP.
Change the type to ExFAT.
Click apply.
You are now ready to reboot in Windows.
Everytime you reboot during the install process you will need to hold option and click the Windows device with the orange USB logo, (Not the EFI orange USB logo). So don't walk away or get distracted, there will be several reboots.
When you are loading, it should say "Using Mac Bootcamp settings to facilitate install" or something along those lines in the upper left corner. If it doesn't you probably selected the wrong boot drive.
You will now start the install process.
You need to select the partion you want to install Windows to.
It will probably be the 4th partition and be about 20Gb less than the size you indicated, and should have Bootcamp in the name.
Select this (it will say Windows cannot install here), and click FORMAT... For the love of god make sure you are on the right partiton before formatting.
You can now install windows on this partition, click next.
This next part is up to you.
It was suggested to me to turn off all updates/autoupdates when it askes during the install operation. This is so you can run the bootcamp install drivers before windows does its thing. After installing bootcamp drivers you can go and turn on Windows updates.
I did this and my SCREEN FLICKERS in Windows. I havent figured out why, im sure its a graphics driver issue, I don't know if this would have happened or not if I had let windows do its updates first, someone will have to be daring and let me know.
Also just a side note as this is my first bootcamp experience and this took me a while to figure out.
After you get windows loaded open the Bootcamp Control Panel and here you can change your trackpad settings to enable two-finger touch for right click.
Good Luck