1)You can squawk standby in the vfr low level route below alt 1250' as it is class g
It's actually Class D, however no clearance or transponder is required to operate in the LLR, so I guess you could squawk standby - but why would you want to turn off a great safety aid?
2)In the VFR circuit, you are mode c (as it is class D airspace) and squawking 3713 as per the textual file.
Not sure what squawk would be allocated, but I'm sure ATC would tell you what to select.
AFAIK there's no requirement to have Mode C available, but it must help.