Here's some great resources and inspiration to explore Death Valley.
https://www.backcountryexplorers.com/death-valley.html
http://www.death-valley.net/forum/index.php
https://www.youtube.com/playlist?list=PL42mpo0Q-wCBNFLMBv29Jp7ADexL_mm-f
https://www.nps.gov/deva/planyourvisit/upload/Death-Valley-Backcountry-Roads.pdf
Here's a video I shot around DV mostly.
I've been going for many years and have spent a lot of time around DV, it's in my backyard. I still discover new trails, mines, cabins and other odd desert stuff. Days or weeks of time there just touches the surface and never gets old.
Since I very much prefer freedom and total silence, I suggest spending more time exploring the BLM and NFS land in Panamint and Saline Valley.
Hit the highlights inside the park if you haven't been for sure and then shed the rules, fees and crowds in DV and wander the valleys next to the park where there's far more freedom that's not as accessible for the masses found inside the park.
No need for an overlander to be paying $35 to camp in a dirt parking lot with the legions of tourists in mini vans and RV's inside the park when there's literally hundreds of thousands of square miles of public land all around to explore and camp on.
While it can be cold at times at higher elevations in March, saying "DV is cold in march" as posted earlier is generalized and not fully accurate. It's common to have a 30-40º difference in elevation at any given time this time of year. It's already starting to warm at low elevation with it forecasted to be in the 70-80's next week on the valley floor. ( I go often this time of year and pay attention, generally going when the weather is bad for better photo opportunities)
It's easy to explore the higher elevations by day and camp in the low elevation valleys at night if you want warmer temps. Or seek out one of the many cabins you can stay in for free and bring wood. Then again, "cold" is quite subjective, and from my experience camping, especially in a ground tent, in the desert comfort is more effected by wind speed rather than just air temps. If it's windy, you camp in protected canyons and not exposed on the valley floor.
Of course weather can change, however you can look at the weather in Furnace Creek for valley floor temps, looks at Trona, CA for 2000-3000' elevation temps and look at Lone Pine, CA for higher elevation temps. You can calculate the forecast for the area by combing info.
Another good weather resource to help with planning is here:
https://www.wrh.noaa.gov/vef/rec/index.php?loc=DV
Chances are, DV and the surrounding areas, at low elevation will be the warmest place in the southwest at any given time.
If I may, I would suggest a National Geographic topo map for DV if you don't have one, the Tom Harrison map will do too. Even better to have both.
Personally, I find the entire Mojave preserve area to be boring as hell and very highly over rated just like Joshua Tree NP, but to each their own. There's interesting geological and to a lesser extend human history in the area, but more exciting to read about than actually explore it, unless you're a rock hound.
I've waisted a fair amount of time exploring there trying to understand the draw or why it's been designated a national preserve... I feel there's much better exploring options all around, especially if time is limited. You can "do" the Mojave road, maybe even buy a sticker to proclaim you concurred the boring road - spoiler alert - it's a mostly straight boring desert track like any other scrubland dirt road in SoCal, and you even will have cell service the whole time from I-15 which is never too far.
I live in the Sequoia NF and you're at least a couple months early to get to most of the notable places in the Sierra's with a massive 160% of the normal snow pack we have this year. Right now the snow level is 3500', with a snowpack level in Mammoth @ 36'.... come back and go skiing in July!
You can download GPX tracks of mine from DV on my site in my sig.
Here's a good Panamint Valley camp spot - Lookout City ghost town, get a good map and it's easy to find. There's a good number of nice rustic cabins to stay in within 10 miles if the weather is ****, or even the Panamint Spring resort if you must.
Have fun!