The trails are fun but really, no big deal.
Can stay in any of the cabins. They are occupied if you see a US flag flying. No flag, it's open. The cabins are part of what's called the adopt-a-cabin program. They are free, but etiquette dictates you leave them better than when you got there. Sign the guestbook, sweep it out good before and after (keeps the rodent droppings and hantavirus at bay) and if you take a can of food, leave one. And don't leave something crappy, like 5-year-old beets.
Barker Ranch (Manson) is closed. There was a fire there a few months ago and it burned. Sad, because it had just been fixed up.
DV is a great place; so much to see it's really impossible to do it all in one trip. I've always worked in regions, exploring the park a bit at a time. Extra everything is mandatory. I usually carry 15 extra gallons of fuel, plus about 6 water. There are only 4 gas stations and none in the northern part. For the supercharged guys, carry octane boost, as the furnace creek station only has regular fuel.
You can only sometimes hit the repeater out toward 395 if you get in a bind. Road conditions and a forum with some updates can be found at deathvalley.com. There's also a link to what's called the Death Valley Morning Report.
Paul, there's so much more here to cover. If you want, give me a call.