Welcome, and great looking Xterra! You are going to fit in great around here. Most of us turn wrenches and work hard to share info to help each other. I'm needing to do both my cats so thanks for the thoughts on unbolting the rear cat. Search for "poor mans flush" on the super easy way to change your transmission fluid. Also search which fluid to use. I've stuck with Nissan Matic S (the only OEM factory fluid I use) and I'm at 255,000 miles without a sign of a problem. But other guys here have had good luck with a couple of aftermarket trans fluids. Oh, and also search for info on the valve covers. The spark plug well has a gasket built into it that fails and leaks oil into the cylinder (which is what killed my cats). Gasket in question is built into the valve cover so you have to replace the entire cover which is cheap from Nissan. You've got a handle on the other main items it looks like! They are great trucks. Be safe.