Electrical – Bathroom circuits code

You are correct that the first two options are allowed by Code (citing from the 2014 NEC here) -- the relevant passage is 210.11(C)(3) along with its Exception:

(3) Bathroom Branch Circuits. In addition to the number of branch circuits required by other parts of this section, at least one 120-volt, 20-ampere branch circuit shall be provided to supply a bathroom receptacle outlet(s). Such circuits shall have no other outlets.

Exception: Where the 20-ampere circuit supplies a single bathroom, outlets for other equipment within the same bathroom shall be permitted to be supplied in accordance with 210.23(A)(1) and (A)(2).

However, this passage only applies to receptacles unless you take advantage of the terms of the exception; putting the bathroom light on a shared lighting circuit is Code-legal as long as the receptacles are on a dedicated circuit.

For the heaters, you can either put them on a per-bathroom circuit as long as they satisfy 210.23(A)(2) by not using up more than 50% of the circuit's ampacity:

(2) Utilization Equipment Fastened in Place. The total rating of utilization equipment fastened in place, other than luminaires, shall not exceed 50 percent of the branch-circuit ampere rating where lighting units, cord-and-plug-connected utilization equipment not fastened in place, or both, are also supplied.

or you can have them on a shared lighting circuit, if you decide to have a separate circuit for bathroom receptacles. Unfortunately, putting them on the same circuit as the bathroom receptacles when that circuit is shared between bathrooms is prohibited by the Exception to 210.23(A):

Exception: The small-appliance branch circuits, laundry branch circuits, and bathroom branch circuits required in a dwelling unit(s) by 210.11(C)(1), (C) (2), and (C)(3) shall supply only the receptacle outlets specified in that section.

You'll need at least one 20 ampere circuit to supply the bathroom receptacles, which cannot serve any other rooms.

You cannot use 14 AWG conductors anywhere on a 20 ampere circuit, all the conductors must be 12 AWG or larger.

The likely course is to have one GFCI protected 20 ampere circuit to serve the bathroom receptacles. One 15 or 20 ampere circuit to supply the lighting in the bathroom (this will include the exhaust fan). And one 15 or 20 ampere circuit to supply the refrigerator. Later when you want to add the microwave, you can install another 15 ampere circuit to supply it.