Yep, subpanels in detached buildings need their own ground rods (and they need to be fed with 4 wires).

Yep, you do need some additional grounding at the cabin. For new construction here is what you are supposed to do. There are some exceptions for existing premises.

Building 1 feeds Building 2 with four wires (ground, neutral, hot (red) and hot (black)), then:
- Bond Neutral to Ground in the Building 1 service panel
- Do NOT Bond Neutral to Ground in the Building 2 panel (may have to remove a bonding screw or strap)
- Connect green to green and white to white in both panels
- Connect the ground bar in Building 2 to a grounding electrode at that building (ground rods, concrete encased electrode, ground ring, etc.)

A single ground rod can be used to ground a panel, but if the resistivity is more than 25 ohms, then you need to add a second rod. However, since it is usually cheaper to just drive two rods 6' apart than it is to get someone out to test ground resistivity, most people skip the test and just put in two rods.

Bonding conductor from the rods to your panel should be #6 bare copper.

Also, keep in mind that even if your local inspector missed this or doesn't care, the phone company can ask for additional facilities to be added above and beyond the building department - telecom grounding is a bit of a black art and sometimes has additional requirements.

Fido has it right with one exception. The ground and neutral is connected at the (Building 1) service disconnect, which may be the main panel there or it may not be.

There's no requirement that the grounding electrode conductor be bare.