I had the same issue and I could update to windows 10 in my HP laptop, but no without problems.
When I updated I had problems with boot (the computer changes the loader to windows boot loader instead of grub) and when I changed to use grub the windows MBR becomes corrupt and I had to solve the problem with a repair image and using the command fixmbr... This solves the problem temporally because each time the bios was updated the default loader changed to windows instead of grub. Nowadays I'm working fine with windows loader instead of grub.
1- Will it work?
Yes, but probably not in the first try.
2- Is there any chance I will break something?
Yes, but with a repair disk and a time probably you could repair it.
3- What do I need to back up to make sure I can go back if something goes wrong?
The most important is to have a repair disk and a copy of all your important data in case you have to reinstall the OS.
Here you have a more detailed guide on how to upgrade.