I haven't had to mess between UEFI and Legacy yet so I can't speak on that. I do know that Windows8 comes with Hyper-V (you just have to enable the role) which would allow you to set up a Windows 7 VM. Depending on the resource requirements of the software in question, that might suffice.
As for dual-booting, I stopped doing that years ago in favor of VMs (first VMWare, then VirtualBox, now Hyper-V as an option). I much prefer to have both OS' accessible to me rather than having to shutdown and boot into another.
Before you do anything though, I'd make a full disk image of the system so you can restore it back to current factory config if something goes wrong or if you just want to revert back. I idle in the ##windows IRC channel on freenode and tons of people come in asking for help on how to restore back. If you don't care about all the poopla that came with it from the factory, you can also just make sure you have the following and do a reinstall yourself:
1) the license key of your Windows install
2) the media of the exact OS version that came with the computer (OEM, Pro, Ent, etc), that's the only version the license key will work with
3) Optional: OS drivers for at least the network card of your system so that you can get online and get other drivers as needed (Optional because the odds are good one of the standard drivers that come with Windows 8 will work fine.