Hello and welcome to the community!
Render times vary quite a lot depending on what's in your scene and of course your rendering hardware. For a couple of examples:
Frames of this animation rendered in about an hour and 15 minutes at 1080p on a 4 core i7 machine:
http://www.youtube.com/watch?v=3_T6zhiI2aMThese were about 1.5hrs each on the same machine:
http://www.youtube.com/watch?v=xetBCFKltZQThis spherical panorama took about 1.5hrs as well (2000x1000):
http://planetside.co.uk/images/terragen3/Spherical_Camera_st_helens_crater.jpgThose examples are all in a similar range of time, but they're just the examples I had at that resolution with render times noted. For more complex volumetrics (clouds), you would probably need to expect higher render times. Lower times would be possible with simpler, terrain-only scenes. I rendered the attached image of one of the Preset scenes in Terragen 3 in about 15 minutes on the same 4-core i7. Detail would probably need to be increased a bit for production, but it would probably still be under 30 minutes.
Render times *for comparable render quality* are generally similar for Terragen and Vue. Vue does "degrade" to much lower quality results in a way that gives you potentially very quick rendering for a rough result. But this can be deceptive as it's not usable in production at that level. For production-quality results, the render times seem to be similar (though the capabilities of the different packages also come into play here, i.e. which one has better volumetric rendering, etc.). For both applications fine-tuning render settings can take some time for ideal results and the best balance of render time vs. quality. We are always happy to help with specific render setting recommendations when you get to that stage.
For hardware, rendering in Terragen 3 is currently CPU-only (which answers the 2nd part of that question too). So you would basically want the fastest CPU you could get at reasonable cost, with a good amount of RAM (RAM is mostly consumed by assets used in your scene, e.g. objects, textures, not as much by the rendering process). If you're buying new hardware for a farm and you're looking for the best price/performance ratio, I would suggest bare-bones 6 core i7 machines with 16-32GB of RAM. You ought to be able to build each one for $1000 or less (CPU is $580USD or so).
Animating weather is very possible and fairly easy to achieve once you understand the basic principles. There is a new 4D noise option in Terragen 3 that can help in particular with cloud "evolution". See here for recent commercial example:
https://www.youtube.com/watch?v=qyDDuSUvXlQ&html5=1&hd=1http://www.fxguide.com/featured/apple-boxes-in-the-car-park-dds-deconstructed-city/Animating cloud density, position, amount of cloud, etc. is all very easy. The same is true for surface maps, even terrain shape. You can animate nearly any setting in Terragen, and the animation controls are all basically the same - you can create a keyframe on most node settings then edit timing, etc. in the timeline. Here's another example of animating cloud settings:
http://www.youtube.com/watch?v=5BwqiD1WPhwTerragen has been interoperable with Nuke for quite some time through import of CHAN format. We also now support CHAN export, so it can be bi-directional. FBX is also supported and that can handle lighting information in addition to camera(s).
We do have a new Spherical Camera option in Terragen 3 and it works quite well as you can see from the above example. There is a bug that occurs with the rendering output in some cases where there will be small areas missing at the edges, but we'll be addressing this in a free update some time early in 2014.
You can import objects in OBJ format, fully textured. Not all material properties are supported (i.e. translucency), but basic material properties and textures are handled well, and most of the rest can be setup within Terragen's own materials system if not directly supported (e.g. reflectivity/specular). We support only OBJ sequences for animated objects at this time. More complex object animations should probably be rendered in another application and composited with Terragen environments.
I hope that helps.
- Oshyan