Sorry, just re-read your post.
To try and answer your specific questions, with my opinion
AngelCakes said:
Going up a hill
Going down a hill
crawling traffic
general day to day driving e.g. 30mph roads no hills.
Going up a hill: regen braking only comes into play when you lift your foot off the accelerator. So in itself not appropriate. It will depnd what is ahead - traffic, or blind summit where you may wish to slow down.
Going down a hill: this is where you would find it most useful, depending on the gradient, your speed etc. just increase or decrease the level to maintain your desired speed. In this situation if it is a long descent you may find yourself increasing then decreasing it quite a bit and find the paddles handy for this. The gear stick just does it in two steps.
Crawling traffic: this is where I would have it on a high setting, you can then just creep and slow up using the one pedal.
General everyday driving: Again very much personal preference about what potential hazards you anticipate and how you want to deal with them. High level means if you see something developing, you just initially lift your foot off the accelerator, rather than having to move to the brake pedal. So you can lift to slow down, if the situation doesn't develop just press it down again.
There's lots of discussion elsewhere about saving energy - I think in general if you want to save energy, where possible you want to free-wheel (ie B0) when you ease off where possible, to maintain your momentum. You don't want to slow down unnecessarily only to expend energy getting back up to speed.
PS A big plus I've found with regen braking whether you use the paddles or not (When you press the brake pedal, initial brake force is produced by regen also) is the lack of brake dust on the front wheels - I'm anticipating brake pads and discs should last considerably longer than conventional braked cars!