I've got 5 kids and went trailer shopping last year. Here are some other factors to think about.
1) If you get a really nice spacious trailer with all the latest electronics & what not, the kids may never actually go outside and see the great place that you traveled to. We have a relatively small trailer for the 7 of us, but we use it as a kitchen and a bedroom. Our living & dining is done outside. Everyone is different, but it's something to think about. Yes, there is room for everyone if it's raining, but if its too nice, good luck ever seeing your teenagers. :)
2) I thought that having their own "space" as you mentioned would be important. We were surprised when my eldest daughter actually wanted to use the couch instead of one of the bunks. Every kid is different. The lazier of my kids like the bunks because they don't have to make their beds first thing in the morning. For the most part, our bunks don't get used during the day.
3) Storage is key. Having a place to put all the kid "stuff" is a huge deal. For my wife & I, having all of the camping gear in the trailer, ready to go, is one of the biggest advantages of a trailer. It makes it so we're willing to go more often. Finding places for the food for everyone, extra blankets, sleeping bags, chairs, baby stuff, etc, etc ,etc... it really ads up.
4) If you are counting on a dinette as a bed, will your oldest be out of the house before your youngest outgrows the dinette? This might sound silly, but do the math. Dinettes aren't very big, and only hold someone who is well under 6'. In my case, my eldest will be well off to college before my youngest is too big to fit on the dinette.
5) Not all trailer bunks are the same length. They range in length from 6' to like 6'9" depending on manufacturer. If you're kids are taller than usual, beware of this! It will be frustrating if you have 3 teenagers (this is just around the corner) , and none of them fit on any of the beds except yours. :)
6) Weight Police Alert! Watch the payload capacity of your truck, especially the weight rating of your rear axle. With all 5 of you & your stuff in your half ton truck, plus the tongue weight of your trailer, you might exceed the payload weight limit of your truck. Don't expect the dealer to sell you something that keeps you comfortably within your weight limit. With most half-tons, it's not the "towing capacity" that's the problem, it's the "payload capacity". You'll have to check your specific vehicle.
Good luck! I'm sure you'll find something that will bring great memories for your family!
