I hiked the Marble Canyon Loop in March 2012.
It was great. I backpacked with my friend who had never been backpacking before and it took us 3 days and 2 nights. We spent the first night at Cottonwood spring. Second night at Dead Horse Canyon.
I have no idea of your backpacking experience, but I would STRONGLY recommend getting 7.5 minute USGS maps and brush up on navigational skills, especially being able to take point bearings because roughly 1/2 the route is off trail.
Another reason I strongly recommend the USGS maps is because backpackers have sometimes gone down the wrong canyon when trying to go from dead horse canyon back onto Marble Canyon. Going down the wrong canyon and making irreversible "dry fall drops" have been known to lead to a 40 foot vertical drop that has often trapped many backpackers.
This group got stuck at the infamous "40 foot drop" and had to fashion a rope out of their clothes:
http://katielambert.wordpress.com/2011/05/23/lost-in-death-valley/
Moral of the story is not to go down the wrong canyon when transferring from Dead Horse Canyon to Marble Canyon.
Another tip I would recommend is to dont be too reliant on the first two smaller springs that come off the main Cottonwood spring. Before leaving the visitor center, the rangers told us that all the Cottonwood springs were running, but my friend and I found all of them dry except the largest one at the end. But I went in mid March, so the water in February should be fine.
In terms of route planning I used Steve Hall's VERY detailed information about Death Valley. Hall's descriptions contain distances and route information.
http://www.panamintcity.com/
Marble Canyon loop information:
http://www.panamintcity.com/exclusives/cmbackpacking.html
But overall, its a wonderful trip! My friend who hasnt event been car camping loved it.