Our current coach is 38' with two slides and is the perfect coach for our use. We do not full time, we love our house too much to let it go. Six months out of the year off and on is our use of the coach. Even with a 38' pulling a tow vehicle can get pretty long and I did have problems getting in and out of a state park off highway 101 near the Redwoods. So I will never try to get into a state park again in California.
If I was to sell my house and go full time then I would probably consider a 45'coach with four slides. You also have to figure what your health status is and whether your spouse would like to live on a coach or in a house after you are gone. Some women do not like traveling around from campground to campground by themselves. Not only that but as you age it gets harder and harder to maneuver one of them big behemoth coaches.