1996 Nissan Maxima my husband's car problem

The gauges stopped working no speedometer fuel and temp are both at full and hot and rpm jumps all over. Bad oil smell as well as exhaust smells really concentrated or strong. It stalls at lights. Engine boggs down when driving in town but it's starting to do the same on the highway driving as well.. Spark plugs changed month. Alt.. Battery.. Please where do we start?