I bought a *****in' products kit to replace my toe board and the front part of my floor pan. I was reluctant to spend the money at first, but I was a beginner like yourself and I wanted something that had some prefab to it to help build my confidence.
But if you don't decide to go with the kit their directions had some good suggestions. First, make sure the cab is aligned on the frame properly. Their kit then supplied some large triangle shaped metal pieces that looked like 3 inch wide by 1/4 thich flat stock bent past 90 degrees. The bend made it to where you could tack the triangle piece to the rocker panel and then to the frame. This will hold your cab in place while your cutting out the floor. Then make sure everything is properly braced!
Its been a long time since I cut mine out but I remember that I had to replace the inner kick panels to so I cut the kick panels and the floor pan out so that I could replace the inner kick panels first and then the floor pan. This way the kick panels seamed in nicely with the floor pan.
Here are some
pics . Not really good pictures but you can see the change between 4 & 5 sort of. I have a ton of pictures of the inside but darn if I can find the digital camera i took them with. I'll look again tonight.
Matt