Congratulations. The only drawback is that coming from a D200 (assuming your profile is up to date) you have a lot of learning to do. That's not a bad thing, since it encourages you to go out and take pictures. Not only that, it gives you an excuse to avoid housework while you master your new tool.
I got mine under similar circumstances. The CFO now gets some new furniture for Christmas.
As part of my study regimen, I made a spreadsheet containing all the menu items (at least as far as I could figure them out). That took about 2 days going through the manual with the camera and laptop to check things out. I recommend that as an exercise, but if you don't want to do that you can look at mine at http://small-farm.org/D4-spreadsheet.xls . It's password protected to avoid accidental modification, but you can open it read-only or use the password which is D4. PS: it's a work in progress.
When I used a D200 I would go up to ISO 400, maybe 800 with some noise reduction. Rarely above that. On the D4 I'll probably use 800 as the normal sensitivity (except maybe outdoors). Playing around over the last couple weeks I get good clean images at 3200, 6400 needs a touch of noise reduction, 12800 is quite usable with noise reduction (I use Lightroom). ISO 50K is OK with significant noise reduction. I wasn't expecting much from ISO 200K, but it will take pictures when the light is so low I can't see much through the viewfinder. At that point you need noise reduction and downsampling to get usable stuff, but you can get something from it.
Live view has a quiet mode which is just a bit less noisy than the shutter+mirror. However, it also has a silent mode, where nothing moves. When I tried it out the camera took about 25 shots before I realized it was working. The only thing that told me it was taking pictures was the green light started to flash. No clicks, no beeps, no sound at all.
A word of warning: If you don't have a good filing system for your photos so you can find what you want quickly after 3-4 years, get one in place now. The D4 is so much fun to use you will be taking 1000 pix a month or more. Pretty soon you will be buried in image files unless you develop a habit of deleting the stuff you'll never look at again. I like Lightroom for its Digital Asset Management capacity. Putting tags on all my photos is essential to me. I also have a program to download pix from the card and give them meaningful names. A month from now you will not remember what DSC_1348 is a picture of, but if it's something like "Suzie's Birthday Party 2012 006", at least you have a clue. Lightroom can change the name for you, but since I got the program before I found out that Lightroom can do that, I've stuck with it.
Before this post gets so long you won't read it, let me conclude with another congratulations and have fun with it. Put some pix in your gallery and don't forget to update your profile.