Having the side open won't increase the risk of fire on it's own but yeah, small fingers and fast rotating things don't really mix well
It shouldn't make any difference for cooling either really, especially as you have a fan mounted on the side panel
which, if it's working properly, should provide more cooling than just passive air would.
I agree with Raid though, check out your CPU cooler and all the other fans are running when you have the system powered on and check the CPU temps after running it for a while. It could just be some TLC but yeah, replacements are more likely a reality.
Also, cable management, it's a thing