How to give thermal stone ability to set things on fire?

[Dr Wikhailov]

My friend asked me to make a custom item: basically a thermal stone, but when charged it can set things on fire like a lighter. I have no idea how to combine stone's heating up system with fuel system from stuff that burns. i'm new to modding, I can easily make characters with slightly complex perks, but custom items are like black magic for me. 

Also: How to properly add custom items to files of the modded character? So they can be uploaded to steam workshop as 1 mod.