Running the live media should not affect your Windows installation in any way. Good luck with the persistence though, (bug 1159016) so you might want a separate USB around just for data transfer. UEFI is just the BIOS replacement, no big deal, but it can come with secure boot,
(which your preinstalled W8 uses), which changes things a lot. Before you do ANY installs to ANYTHING (like another USB), backup the EFI files, visible in /boot/efi (they should all be under directory EFI, and are just files). There are so many machine specific problems, that I hesitate to predict what your Lenovo will do, but it is good to have a set of files to restore if your pc suddenly cannot boot W8 anymore.
boot-repair is a tool which fixes up some installer issues, and is a good thing to have around. If you have working persistence on the live-media, you can install it:
sudo add-apt-repository ppa:yannubuntu/boot-repair
sudo apt-get update
sudo apt-get install boot-repair
Or download and burn an iso with it preinstalled from
Linux secure remix