Same thing as you did before Alan mate, wherever they'll fit. (Within reason of course.
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Top and bottom of the door, East/West walls, North/South, doesn't really matter as all you're doing is providing fresh air ventilation and possibly preventing dew point condensation if the heating won't always be on. (I have small heaters always set to 5'C in my sheds to prevent frost damage and condensation.)
In my metal shed I have the vents at the roof apex front and rear as well as insulation on the metal roof to prevent condensation.
The only thing I'd suggest is if you have a perennial wind direction put your vents on the opposite direction, same thing for rain splash back making sure the vents won't let water in.
Dust can be the enemy as regards condensation holding more moisture for longer than you think. My missus is always 'upgrading' her hairdryers and I nicked a couple just for the sheds so that I can blow down all the surfaces. (Much easier than traditional 'dusting'.
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If you have vents that can close for heating purposes then just make sure that when you leave the shed you allow a fresh air flow through and the temperature to come to equilibrium with the outside. That'll help with condensation....we exhale/sweat a lot more than you'd think!
Been doing that for years and not a single item has been damaged by typical rust on any machinery or electronics.