Is there machine that is capable of using mana to power spells or something similar to a spell?
No spells in traditional sense, but technology. Think of hypertechnology of Technocratic Union in WoD. Technically Magic, but behaves like advanced technology.
Since magic is just a fuel source and you are limiting yourself to a preindustrial revolution technology level what would teh difference to humanities ability in the place if they were to not have magic fuel and used some other fuel?
Would they have similar tech levels yet operate on a slightly larger scale due to greater ease of fuel access?
How do deities get domains? Do they ever overlap?
Since there is no steam engines, without magic all those clockpunk devices and goodies would stop working, but otherwise the technology level would not drop drastically. Cannons and firearms are independent of magic.
It matters what concepts are related to a given deity. Followers shifting their perception of a deity might even change it to an extent.