Which PC model are you buying?
As for reassurances, in general, I adore my non-slide 2351 (solo full-timer with dog). I find it to be solid and comfy and lovely. As I walk around campgrounds, mine is among the smallest around, until you get to the Class B vans and then the tent campers. I love that I can maneuver into many spots that longer, taller units could not. I love that low bridges and tree branches don't freak me out. I think those cab-over-beds are nice for kids, for sure, but I believe they come at the expense of a low profile.
You said this is going to be your first RV. My question is, is it going to be your family's first experience with camping? If you have been tent-camping and roughing it, then even a small motor home will be luxurious in comparison. If you haven't been camping at all much, then, yes, two adults and two children might be a challenge compared to living in your house. But I'm not sure going an extra few feet in length will solve that. Also, if you will primarily be using this in fair weather, your children (especially as they get older) might well get a kick out of tent camping on your site while you and your wife enjoy the amenities and comfort of your cabin-on-wheels. There is also the question of how you like to camp... Are you outside around the campfire and on lots of walks and stuff? Or do you enjoy being cozy inside with a couple of TV's and--in some cases!!--a fireplace?
Last note, I spoke to Kermit today re a small leak that I've discovered in my rig. As others on this forum have experienced before me, the customer service that you get from Phoenix USA is personal and of extraordinary quality. I don't know how the other company(s) you are considering compare, but I believe this is a really important consideration when buying something so expensive and so likely to have issues crop up as it is bumped and jostled over hundreds and, perhaps, thousands of miles.
Oh, and I am at a campground south of Alexandria, VA for at least the next few weeks. If you have not seen a PC yet, or even if you have and you'd like to see another, you are welcome to stop by. You can find my contact info under my profile.
Whatever you decide, I hope you and your family enjoy many miles and many, many wonderful memories in your new rig!