Welcome MAxz1985!
Avoid using automatic effects such as these, except for specific details. The only way you can draw the shading and lighting is with a soft brush at low opacity. Add a tiny bit of light/shadow, look at it and compare with pictures and then add some more. Keep doing this until you're satisfied with the results. It can be a long process to get the lighting and shading right but it is probably one of the most important so you should be patient.
In general, use as many layers as your computer will handle (many layers = larger filesize). I assume you're using Photoshop or Gimp. BTW 3700 px wide is good enough IMHO. I work at that width. I can print in A3 and I still lose much of the details, so don't bother with anyhting higher for the moment.
There are colours palettes available on the site. You can also ask John (JMSmith), our local guru.

You might start by asking him whether that Lancaster plan is valid or not. It seems a bit "fat" to me but I might be wrong.
Practice makes good. Practice, practice, practice, practice,practice, practice and then more practice makes perfect.
Good work and keep us posted!