I want to run windows 8 on my IMac, what version would I need?

Any version you wish. Understand that Apple does not support Win8 completely. You need to read the Boot Camp documentation in Boot Camp Assistant. Note that Win7 is a better compatibility choice.

You need to upgrade to Mountain Lion, however.

Upgrading to Mountain Lion

To upgrade to Mountain Lion you must have Snow Leopard 10.6.8 or Lion installed. Purchase and download Mountain Lion from the App Store. Sign in using your Apple ID. Mountain Lion is $19.99 plus tax. The file is quite large, over 4 GBs, so allow some time to download. It would be preferable to use Ethernet because it is nearly four times faster than wireless.

OS X Mountain Lion - System Requirements

Macs that can be upgraded to OS X Mountain Lion

1. iMac (Mid 2007 or newer) - Model Identifier 7,1 or later

2. MacBook (Late 2008 Aluminum, or Early 2009 or newer) - Model Identifier 5,1 or later

3. MacBook Pro (Mid/Late 2007 or newer) - Model Identifier 3,1 or later

4. MacBook Air (Late 2008 or newer) - Model Identifier 2,1 or later

5. Mac mini (Early 2009 or newer) - Model Identifier 3,1 or later

6. Mac Pro (Early 2008 or newer) - Model Identifier 3,1 or later

7. Xserve (Early 2009) - Model Identifier 3,1 or later

To find the model identifier open System Profiler in the Utilities folder. It's displayed in the panel on the right.

Are my applications compatible?

See App Compatibility Table - RoaringApps.

ll of them are able to be run with bootcamp now after the 10.8.3 update.

I may be out of order in adding this point, as it is pretty clear on the Boot Camp instructions, but you do need a full install, and not an upgrade install disk for a partition that has not previously contained Windows. If you buy a Windows 8 disk in a shop (at least in my country) it is almost invariably an upgrade version. The Microsoft help pages suggest using an OEM System Builder version to put Windows on a Mac partition. Even so, I have found this morning that, if you create a boot disk, following the instructions with a previous download of Windows 8 for another computer, Boot Camp will recognise it as a full install disk. All you need then is another key.