I've never welded before either. I own a flux core welder. I've used it a couple of times for more utility-type welding on thick pieces of metal, but so far I've been unsuccessful in getting sheet metal welded. I have succeeded in burning a lot of holes in sheet metal, though. Scrap stuff, fortunately. From what I understand, welding sheet metal is kind of an advanced technique, not something to start with. And, flux core welders can produce usable welds, but probably not by novices. The advice I've gotten is to either get some welding instruction and get pretty good at it, farm it out to someone who knows what they're doing, or buy a MUCH better welder (MIG at least, or TIG) and get some basic instruction before trying it.
I'm putting off the welding on my project for now and working on the engine, until I can either find someone who can do what needs to be done for a reasonable cost, or get some training so I can do it myself. I'll probably end up farming it out, because my object is not to become a skilled welder but to get the car finished.
Just my $.02 worth, discounted somewhat because I'm basically in the same boat you are.