You can do it, it is like any other trade.........once you learn the tricks, you are good to go. To get those "tricks", purchase books, videos, etc., ask questions, and don't worry.........it is NOT rocket science! The guys here in Moparts are an endless supply of help. You can tack weld all of your floor sections, then seam seal, but you should skip weld your quarters solid. That is, weld them solid using the "skip weld" method of small 1/8 to 1/4 inch welds skipping back and forth from hot areas to cool ones, to minimize wharping. A beginner is not going to be able to butt weld a quarter panel, so a 1/4 flange will work quite well, with seam sealer inside to hide it. And don't weld anything until your trunk lid lines up good, and your door lines are good, and everything is as close to perfect as you can make it. I use 1/8 inch screws, they make panel holders, but screws have served me well for 20 years to hold everything in place, along with a couple of dozen severely beaten up, scummy vise grips!!!!!!