The recommendation to only put four additional receptacles beyond the GFCI is simply to keep each circuit to five or less (duplex) receptacles. Not a code requirement, just a way to help avoid too many devices on each circuit.
Which is really pulling a number out of thin air, because it all depends on what might get plugged into the receptacles and operated at the same time.
For non dwelling, non hotel/motel room, the best guidance is found in NEC 220.14(H), (I), and (L).
(H) Fixed Multioutlet Assemblies. Fixed multioutlet assemblies
used in other than dwelling units or the guest
rooms or guest suites of hotels or motels shall be calculated
in accordance with (H)(1) or (H)(2). For the purposes of
this section, the calculation shall be permitted to be based
on the portion that contains receptacle outlets.
(1) Where appliances are unlikely to be used simultaneously,
each 1.5 m (5 ft) or fraction thereof of each
separate and continuous length shall be considered as
one outlet of not less than 180 volt-amperes.
(2) Where appliances are likely to be used simultaneously,
each 300 mm (1 ft) or fraction thereof shall be considered
as an outlet of not less than 180 volt-amperes.
(I) Receptacle Outlets. Except as covered in 220.14(J)
and (K), receptacle outlets shall be calculated at not less than 180 volt-amperes for each single or for each multiple
receptacle on one yoke. A single piece of equipment consisting
of a multiple receptacle comprised of four or more receptacles
shall be calculated at not less than 90 volt-amperes per
receptacle. This provision shall not be applicable to the receptacle
outlets specified in 210.11(C)(1) and (C)(2).
(J) Dwelling Occupancies. In one-family, two-family, and
multifamily dwellings and in guest rooms or guest suites of
hotels and motels, the outlets specified in (J)(1), (J)(2), and
(J)(3) are included in the general lighting load calculations
of 220.12. No additional load calculations shall be required
for such outlets.
(1) All general-use receptacle outlets of 20-ampere rating
or less, including receptacles connected to the circuits
in 210.11(C)(3)
(2) The receptacle outlets specified in 210.52(E) and (G)
(3) The lighting outlets specified in 210.70(A) and (B)
(K) Banks and Office Buildings. In banks or office buildings,
the receptacle loads shall be calculated to be the larger
of (1) or (2):
(1) The calculated load from 220.14(I)
(2) 11 volt-amperes/m2 or 1 volt-ampere/ft2
(L) Other Outlets. Other outlets not covered in 220.14(A)
through (K) shall be calculated based on 180 volt-amperes
per outlet.
As always, you would need to have the complete code in front of you to understand all of the ifs, ands, and buttttttss involved in it.
Essentially, 180VA per yoke or strap. If the outlet has four or more receptacles then you use 90VA per receptacle.
Thus, a 20amp branch circuit supplying a string of receptacles would be 20x120=2400 divided by 180=13.33 yokes per circuit, or 13 duplex receptacles.
Reality is, I have no more than four receptacles on a given circuit, but but this is due to placement of the receptacles (somewhat limited in a steel building) and the desire to put the receptacles on each wall on a separate circuit(s). I have two duplex receptacles in a deep 4x4 box at each column or post of the building, and in three odd places. Each box has two separate circuits supplying it (NOT multiwire circuits).
Charles
