Although receptacle ONLY circuits in residential structures don't have limitations unless otherwise restricted, lighting circuits and those that contain both lighting fixtures AND receptacles DO.
Lighting loads are demand and/or continuous loads. Old 210.6 (few AHJ's have adopted 2005 and since its re-codified on many issues, "luminaires" included, AND i'm in a hurry, and my AHJ hasn't yet adopted it so I'm not that quick to pull the newer cites up out of my brain yet, I'll skip the newer references).
210.6 limits combination circuits to any COMBINATION of cord and plug connected loads WITH lighting fixtures (now referred to as "luminaires") at 120 volts, nominal, WERE restricted to 1440VA in dwelling units (old 210-6) irregardless of whether or not it was a 15A or a 20A branch circuit. There are many reasons for this. A) conductors must be sized and not designed to be loaded above 80% of their capacity and luminaires frequently have wiring of 16 AWG and 18 AWG, and B) overcurrent protection devices are not to be designed to be loaded above 80% of capacity. This is a code-required designed protection for demand times and still not cause an over-load situation. Additionally an Overcurrent protection device (fuse or circuit breaker) is not designed to open the circuit until the power drawn exceeds its rating, and tolerances for power and time are based on the circuit to be designed on this premiss. cross reference the ampacity tables, etc. for 18 and 16 AWG and the answer becomes clear regards to a combination circuit with luminaires not being allowed to be 20 amps. There is a SPECIFIC exception allowing ONE such luminaire in a dedicated 20 amp BATHROOM receptacle circuit and it too has limitations as to the power rating of what is installed.
GFCI receptacles in garages, detached residential structures (more strict) and attached and required to be 20 amp circuits? You know the references for these conditions as you too have cited them. this is building a garage that never existed before and we don't know at thispoint if it is attached or detached, only that it will be "facing" the alley. As you know accessible and not otherwise dedicated receptacles in either scenario must be GFCI protected. (exceptions are the overhead outlet servicing a garage door opener perhaps, and one not readily accessible servicing a refrigerator or freezer for example. GFCI is required 210-8(a)(1), (2), (3), (4), (5), (6) and (7), 210-8(b) in Residential bathrooms, storage & work areas, all exterior sites, garages, unfinished basements, kitchen counter tops, wet bars, boathouses and with 2003 & 2005 all areas within 6' RADIUS of a sink, and a dedicated GFCI protected receptacle circuit in laundry rooms in addition to those supplying laundry appliances. 305-6 (a) and (b) All permanently-wired receptacles used for power during construction or remodeling.
IF the garage is detached there are limits as to the kva and number of receptacles that are invoked that don't exist if the garage is ATTACHED to the home.
Since the OP has left this thread, I don't know why you continue to challenge, as I have referred you before to the 1440va and 80% (converse of 125%) demand load limitation before but you keep missing it. I know YOU know, Doug, about the GFCI and 20 amp requirement as you have cited it before, and surely you realize that there are additional restrictions regards to DETACHED garages.
Of course even more interesting is if she'd like to beable to control the exterior lighting on the garage, IF detached, from the house, but why introduce a factor that the OP hasn't suggested.