Is it hard to replace a coil? I'm told I need one for a 94 lumina. Is this something that I can do at home?

It's very easy. 3 wires and a bolt. 1 large wire to the centre of the coil, simply pull off by the rubber cover, the 2 smaller wires are the important ones, one goes to the negative (-) terminal and the other to the posative (+) terminal. If you pull off 1 and connect it to the new coil and then do the other wire you can't go wrong. then undo the bolt or screw that holds the coil and slide it out, replace the new coil, tighten the screw or bolt and connect the big centre wire.