Good question Neil.
Build a small room that has lighting which replicates what you want light wise and just stick a layout in the middle of it - that should hopefully avoid the issue of rain in Wales that Jordan failed to address
In all honesty and in my opinion, its impossible to answer the question as there aren't enough defined constraints. Of the two concerns, which one will you compromise on first? How are you going to define each of 'open and airy feel' and 'dawn to dusk'?
Is dawn to dusk a combination of light intensity, colour, angle and direction of source and should it be confined to the model or do you need a background to bring out the transition from light diffused pinks and blues through to harsh yellows to inky blues at night? Is dusk defined just by the light, or the length of the shadows, by silhouettes, lighting on and in the models themselves?
I note you said open and airy
feel, are you going for a Shell Island presentation that achieved that aim, or a layout where the physical edges are blurred and therefore you loose the dimensioned feel in a large space? Are you going to be using colour, track density, subject, composition and relative heights, widths and physical dimensions of the models to carry the feel you want? Is it going to be an eye level presentation so you can control horizon and perspective, or table top, or an island of colour and activity in a sea of neutrals? From how far away does the layout need to convey its feel, across the room, 20 paces, three feet or 6 inches?
To my mind once you have defined what you want to see and experience in front of you, you can then go on to work out what is going to be required to achieve that. It is then a matter of letting the brain work out the best way of combining those requirements which will give you the experience you desire.
I know that doesn't help much, but we could design a light rig for you that is either a single pole with three different bulbs on just to give you colour variation, or it could be a graceful arch containing a multitude of lights to allow you to present changes in colour, intensity and direction. Both would do 'dawn to dusk', but with varying levels of success and replication of real life, until we know where you wish to sit within that spectrum its a bit like guessing the length of a piece of string you can't see
The above is not intended as criticism of the question, just a response to the 'creative hand grenade' lobbed over the wall
I'm an engineer, I like to have defined boundaries to the problem as that is what leads to solutions and innovations,
for me. I haven't written the above with any desire for you to answer the questions, but hopefully something might nudge you off down a particular route. We are all different, take different approaches and I like that. I do try to learn from it - but I am an engineer
Steve (I'm on the knack spectrum but it is not full blown for me
)