360 spherical panoramas - what body+lense to use

Hello everyone!

Disclaimer: I have a rather limited knowledge in digital photography, so if I use the wrong terms, please excuse me(feel free to point out my mistakes when posting an answer, so I can improve).

Me and my colleagues are preparing to start work on a rather big project. What we're planning to do is more or less what Google Trek does(creating street view like virtual walks of hiking trails). Except for we will limit ourselves to hiking trails in Bulgaria. We'll also collaborate with the scouts here in order to refresh and fix-up the trails before we photograph them.

Now, we're currently at ground zero and we are trying to figure out what body+lense combination to use(we have a rather tight budget). We're pretty certain that in order to create spherical panoramas, we'll have to use fisheye lenses, so that when the rectangular image is placed on the inside of the sphere, it doesn't look squished together at the top and bottom parts of the sphere.

One of the recommendations we've had so far is to use 3 Canon EOS 6D cameras with Sigma Fisheye 8mm f/3.5 EX DG fisheye lenses. The idea being that the 6D is a Full Frame body, so we won't lose any real estate from our field of view.

If you're wondering why we need multiple cameras, the explanation is quite simple - we don't want to stop and take multiple images for every point on the trail(considering that most trails are 1-3 hours of normal paced hiking, having to stop every 50 meters or so would just take way too long).

Now, about the setup mentioned above I have two questions:
 - would the three cameras be enough to capture a full 360 panorama(I assume so, but I'd like to get someone else's opinion)
 - does the 6D support USB tethering? The whole thing will be automated, so we need to be able to take pictures at certain intervals through a laptop.

Ideally our cameras budget shouldn't go over $8000(the above setup would come to around $7000 if bought from the US, but it comes to exactly about $8000 when bought here in Bulgaria, or delivered half way across the world...).

Do you have better suggestions for a setup? If so, what? The main points are the budget, the ability for USB tethering and that less cameras is better for us(the Canon setup starts at 3.5 kg bare weight, and we'll have to carry other equipment as well;).

I'd appreciate any feedback,
Nikola