Awesome, you'll have so much fun I reckon.
I don't have kids yet either, but may try a Big Dummy/Freeradical when that day comes, or even a Bakfiets type as you can keep half an eye on the kids all the time then.
I treat the Ute as our estate car, trying to get more carless (?!) all the time.
Any load on the deck would be quite high (700c wheels innit, weird choice?), and I've avoided putting a dog crate on the top there for that reason. But it would be fine for the bulky lightweight stuff, like camping gear, big parcels, oodles of bog roll on the supermarket run etc.
Saying that, I have seen people transport kids on Utes:
"Mooooom, dad's bum's in my face...and he ate BEANS"
Kona-made luggage options are still limited, but that's cool if you're handy with stuff and can make yr own. Would ideally like to get/fashion some caged panniers that would collapse in, one big enough for our medium/small dog.
"Every time I see an adult on a bicycle, I no longer despair for the future of the human race" - H.G. Wells
"When I was a kid, if you saw an adult on a bicycle they either (A) stole it, (B) were drunk, or (C) had lost their driving license, or (D) A, B and C" - Malvern Rider