The panel is integrated and cannot be replaced. However, please try to clean the panel with a cloth and CIF cream.
These are a cold white colour
The batteries for the Thea can be found here
The lumens of the light cannot be changed
The batteries are in the panel. They are AA rechargeable batteries and it doesn't matter on the mAh as long as the voltage is 1.2 volt. So any AA rechargeable will be ok, as long as it is 1.2v.
It will depend on the effect you are after to what light would work best. Our spot lights page shows the lumens (the brightness of each light) to help you decide. Remote panels would allow for you get more direct sun so maybe look at the globes too. As long as the light from one spot light doesn't hit the panel of another you can space them as you'd like. I'd suggest anything from 50cm (20inch) to 2m (6"half) apart.
The nearest alternative warm white projection light we do is the Evo SMD however the Tunbridges are a warm white alternative style light that maybe of interest.
The Thea produces 80 lumens, there aren't different length poles available.