Most pee pads are in the 18-24 inch size range. I like the
Simple Solution Jump Start, they really attract puppies to use them. I don't know what others do, but I leave a pad out for several days unless there is diarrhea that cannot be easily picked up. I pick up the poo as soon as I see it. I believe that the scent of urine on the pad attracts the dog to use the same place again and again. Once it starts to smell I toss it. I usually have 2 or 3 pads out at a time so it is not as gross as it sounds. Pee pad training is a good idea if you ever plan to take your dog on a road trip. If you sneak him into a motel, it will be hard to take him outside to potty.
If you let him go on a bare floor, he will get the idea that he can go on any bare floor, and that could create problems. Using a pad teaches him to use a pad, no matter where that pad is. I can also tell you from personal experience, if your baby ever has leg surgery and needs help to go potty, a pee pad is certainly much easier than putting on cast covers so he can go pee outside.