Make sure you get a 91-92 because of the whole speedometer cable thing. Electric vs. cable. Make sure you hook up your tach. correctly. And I understand your new, but try and search. There has been about 3 threads on this subject alone in the past week. Sorry for seeming like an ass if that's how you take it, my apologies. Someone will be able to help you out with wiring and and all fun stuff!! I'm not experienced with it personally so I'm not that big of a help.
Look at Sentra.net. Search there. Their forum is a lot bigger, which means more threads. Also, myself and others would probably reccomend going with an SE cluster instead of SE-R. They'll probably be able to answer most of your questions over there. But remember, be kind and search first! You'll probably get rammed over there if you don't.
I switched my cluster from a 91 SE. The wiring is not even close to plugging in. You have to mark the wires and then find which ines go where. The colors are not the same either. It takes time to do this, but lable every wire and know what goes where. Use the Wiring diagram in the facotry Nissan manual.
Why would you put the cluster from an SE into an SE-R Chris? That's why your wiring probably didn't match up, the GA16DE and SR20DE wiring might be entirely different since the ECU to Engine wiring is.