Anybody can do it, so they say.

I have a 78 C-Gull, which you guys probably already know, is a fiberglass walk-thru sport boat. I want to replace the seats with fold down seats. The seats that are on it, are lounge seats, but they are not mounted to anything and are in desperate need of replacement. The previous owner just replaced the floor and carpet with treated plywood.
My problem is that I'm getting too much info on what to do, and what not to do, to accomplish this project. This is my first time and my first fiberglass boat.
Can someone give me some guidance on this project. Some say that I can use self-drilling screws and go right in the floor, while others say that I need to get under the floor to apply bolts and a base plate. I'm thinking that the self-drilling screw method would be very temporary and result in me having to do this job again, but I'm guessing. Any input would be helpful, because I'm planning to be on the Gulf Coast by Saturday morning.

Would it be feasible to also put a seat on that step between the cushions and right before the windows at the bow.