spectacular lightning and FX for a simple exterior scene

[zsero]

One of my friends just asked me to do him a special architectural viz animation where the scene is very simple but the visualization needs to be very spectacular. All the animation would be camera moving around a building (helicopter view) and the scene would be in the middle of urban area. The maps of the buildings around are not known, so I think the environment will be a textured background.

So my task is to make a very simple building's visualization spectacular, and this is why I came here to composition, because although I haven’t tried any of these software I really think I have to go this way. I think I will use either AE or Combustion. (Nuke is unknown where I live :-( )

What do you suggest me, what makes a scene very spectacular but is not very hard to do with these software? I am thinking about a windy, snowy scene turning into a clear sunny afternoon with a sun shining through clouds OR the same with rain instead of snow and maybe a rainbow at the middle. Maybe the sun could go down for a sunset.

I thought about the following techniques (correct me, I haven’t used any compositing before):

- rendering in max with vray (thanks Chris for your irradiance map session!) using HDRI for lightning.

Question: how to do the transition as the weather changes? AFAIK the vray HDRI map doesn't support HDRI FLIs, so I cannot animate HDRI like a normal map. Do 3 different renderings (for different lightings) and do the transition in the composing package? How to do the "sun coming out behind the clouds" thing? I can use a HDRI map for lighting but I have to use a direct light for the part when the sun shines. Animating the light multiplier makes the irradiance map caching unusable, doesn't it (I need to recalculate ir.map for every frame)?

- composition of some spectacular sky: what is better, to use max to render the background, or leave it to the comp. app using 3D compositing?

- rain or snow could be a PFlow and rendered in scanline and mixed in comp.

- shining sun is clearly a post-processing, as suggested former in this forum.

What app. do you suggest for this particular application? Do I need to look for something like AfterBurn or DreamScape or max + HDRshop + combustion or AE is enough for the job?