I've seen gutters that look worse than that with no other rust on the van. They go first for some reason sometimes. It certainly looks salvageable to me. Unless you really like messy bodywork just look at spending a grand or so and having it done. Get them to Raptor/Rhino/bedline it and be done. Sounds like a good find otherwise.
Check for any moisture or signs of it in the front floorboard area. Minor rust on the roofs of these vans often presents a leak under the windshield seal and you won't know you have one except for wet carpet under the front mats. I'd pop the trim in the footwells and fold that carpet back as good as you can looking for rust or signs of moisture.
and welcome. Show us some more pics if you like and you'll get some more opinions and pointers.