This may be posted already? If not, wha hey! It clarifies some ambiguities in hut guidance as did my successful Appeal against Argyll. Dig around here for post about that.
Internal floorspace is not external footprint. Floorspace has a definition in planning and is the usable floor, internal, with a certain min headroom.
Sleeping platforms are permitted and can add up to 8m2.
A site is what is being approved and a site is not limited to a single hut. The design / look is secondary although gets talked about as if the primary planning consideration. It is not. I have 2 huts approved on a small site: hut, toilet hut. Each hut can be the defined size (30m2).
The size of the site is irrelevant. My defined site is 8x8m. I recommend keeping it small. It reduces complications.
How you get from road, rail, loch, sky to the hut is irrelevant.
External porch and decking is not floorspace.
I have read of multi-storey thoughts. Not excluded but does not gain floorspace: floorspace is the limit, not height and footprint.
Renting. Not excluded. Recreational does not mean non-commercial. Guidance is clear.You will, however, have to consider STL requirements and obtain planning unless it is an Excluded type. Most huts will be Excluded type under the "bothy" definition but you may get an ENO threat.
Note that STL legislation does not care whether the property is rented at zero income or for profit. It is "use" that is legislated for.