In accordance with any instructions included in the listing or labeling [110.3(B)].
 

This isn't defined in the NEC [110.12]. But a qualified person is expected to know what this means. In many cases, the NEC will provide an occasional clarifying requirement, but don't read something that isn't there.
 

Close them [110.12(A)]. This is one of the most common Code violations.

The first is that the equipment must be firmly secured to the surface on which it is mounted. You can generally achieve this by simply using the manufacturer's mounting hardware. The second is you can't use wooden plugs as a means of mounting.
 

Yes, but only as allowed by 110.14.
 

The temperature rating of the connected equipment [110.14(C)(1)]. But see Annex D(2)(b) for an application where this isn't a limitation.
 

No. Part II applies to 600V and under; Part III applies to over 600V.
 

Yes and no. Three feet is the minimum. The NEC provides other space requirements, depending on various factors. See the tables in 110, which you will also find in OSHA Part 1926 Subpart E.  Operational, maintenance, and other considerations may cause you to provide even more space.
 

Guard against accidental contact, guard against physical damage, and provide proper signage [110.27].
 

They must be corrosion-resistant [110.79].