@User What's the metal used in the process? (metal1) Is it Al?

Aluminum for m1 through m5, with a Titanium Nitride (TiN) layer for "local interconnect" (under metal1) and a Copper RDL layer (done by a 3rd party service, so the specs we currently have for RDL need to be revisited).

Speaking of the local interconnect. Can it be treated as just another metal layer or is it truly cell local only? If the second, what's the max effective length?

There is a weird and hard-to-implement DRC rule that restricts uncontacted local interconnect to an aspect ratio of 10:1. Possibly you can get around that rule by specifically declaring the local interconnect to be a resistor. Regardless, any long wire of local interconnect should be treated much the same way as you would a long wire of polysilicon: Something to avoid unless you're okay with a high resistance. TiN has a resistivity that is about 1/3 of polysilicon, but that's many times more than the resistivity of any metal layer.