Don't underestimate the Chrysler 420A engine. I have a 1996 Eagle Talon that has the same motor and I'll take it over the 2.4 any day since the 420A has DOHC and the 2.4 is just SOHC. Given the opportunity though, I'd say throw the 420 out and get the SRT4 motor although I'm not sure if they had those in 96. As for some performance upgrades, a good set of exhaust headers and a cold air intake will help it. Don't get a short ram intake because there is too much heat under the hood. Prothane motor mounts are a good upgrade from the stock rubber mounts and at a fairly cheap price. I picked mine up for $80 for all four mounts. If you're more for enjoying the ride than performance, go for Energy Suspension. Same thing just made with softer polyurethane.
Above all else, and without it everything else is irrelevant, invest in a factory service manual. I'm not talking a Haynes or Chilton. I mean the actual factory service manual.