Yes pretty much everything, at any point in the game your factory should be able to run until it empties an input patch without you doing anything (after red science, early game is a bit manual).
Definitely don't shove chests in the middle, they just make problems
Generally you would put a splitter down and send half the iron to gears, half to whatever else, when you need to use more iron, put another splitter down and take another half.
If you're not using all the gears then the machine will backup and stop consuming plates and more of your plates will then flow the other side of the splitter