Mentioning the year would help, because the VG33E is very different than the VQ35DE. Sitting is never good on any vehicle and there is a good chance that stale gas could be the problem. If it's the VQ, an idle air volume relearn may be necessary. Fuel pressure could be an issue. Rodent damage to wiring can cause problems. A sticking IAC valve could be a concern. Also, when sitting, rubber or neoprene seals, like those used in the master cylinder, brake calipers and automatic transmissions, can be affected. The fact that is fires up is a good thing, so I would concentrate on the fuel system for now. Also, once you get it running, I would service the transmission fluid, as well.