Hmmmm. Well, not one of us pops out of the womb with the skills to weld, fabricate, etc... So in that sense you aren't crazy at all, everybody has to start somewhere. If you have the time and an adequate space, and a willingness/desire to learn and spend some money on tools and stuff, then go for it.
However, while you may not be crazy in thinking you can tackle that, I can't help but wonder if you are perhaps a little more crazy to not believe that there is rust beyond what you can see. If there's rust there I can't help but wonder if there is other stuff hiding down in the rockers and places like that. I'd just suggest being VERY cautious in looking for other rot and at least going in with your eyes wide open, or be willing to walk away if it's more than you are comfortable taking on. I spent many weekends over the course of three years doing all of my metalwork, so ask me how I know...
My "rejuvenation" blog: http://65tomfoolery.wordpress.com
'65 Alfa Giulia Sprint GT, a long way to go still….