If you're doing a lot of "action style" videography in your marketing work, then I would still recommend a true video camera, as it tracks motion and autofocuses much faster. Something along these lines -
Canon XA10 HD Professional Camcorder 4922B002 B&H Photo Video
However, if you're doing shots where the action within the scene is fairly sedate - still shots, interviews, people walking (not running), etc. - then you can go with a DSLR. If you want Nikon, I agree with SFIND's suggestion of the D750. If you prefer Canon, then I have to recommend the 70D. It's fantastic and even does a decent job of autofocus tracking, closer to traditional video camera quality.
You'll also need a versatile lens, and the Canon 70D is being packaged with a really nice 18-135mm STM lens that would be perfect for both portrait style interviews and traditional b-roll. The STM lenses are ideal for video because they're all internal motors, so they're super quiet.
Regardless of what you choose, you absolutely need to pick up external microphones. The onboard audio for any video camera and ESPECIALLY any DSLR is just not professional or good enough. If you're doing a lot of sit-down interviews, you might want to explore a lavalier microphone and pack. If you're doing a lot of walking/talking interviews and have a helper, you might want to go for a boom microphone. And if you're doing man-on-the-street interviews, you might want a traditional stick microphone. Or all three options.
Finally, you'll also want to invest into a quality tripod. And if you're looking at a lot of indoor interviews, a small light kit is encouraged as well.
As far as editing, I recommend Adobe. Adobe Premiere will do everything you need and Adobe products work on both PC and Mac. Plus, you have seamless integration between Photshop and Premiere. If you have a Mac and prefer Final Cut, it'll cost you $300. If you want the latest and greatest from Adobe, you can get the Creative Cloud version of Premiere for $19.99 a month or about $239 a year. Or, you can go cheap and get Photoshop and Premiere Elements 14 for $115 from Amazon. Elements is a scaled down version of both services, but it still lets you edit camera raw photos and do fairly decent video work. I've used both and have zero complaints.
In short, sites like bhphotovideo.com and adorama.com should be your favorites. You might be able to find sales at other places. Beware of buying camera gear on Amazon; just make sure it's fulfilled by Amazon or from the manufacturer directly. Some third-party vendors are a bit shady.
Here's a potential shopping list:
Canon 70D DSLR with 18-135 mm STM lens -
$1,299 from B&H
Magnus tripod (converts to monopod for on-the-go shooting) -
$89.95 from B&H
Polsen Lavalier microphone -
$22.95 from B&H (wireless are much more expensive, and this one goes right to the audio jack on the camera without an adapter)
Rode VideoMic Pro shotgun microphone -
$189 from B&H (worth it to have a back-up that captures all sound if the lav mic fails)
Adobe Elements 14 Bundle (Photoshop & Premiere) -
$115 from Amazon
Basic Flashpoint light kit -
$109.95 from Adorama
Total cost - $1825 plus taxes and shipping.