Highly Adjustable Long Reach Wall or Ceiling Light

If I use my own shade for colour purposes, what is the maximum weight it must be? You give ideal dimensions but not the weight though you say the weight is important. Also, what sort of fitting should my shade have?
Yes, you can use your own shade and we give guidance on the dimensions to help you decide if your own shade will work. As with any flex or wall bracket weight is a consideration as you would not want the arm to be struggling to move with something heavier like glass for example. However if your shade is fabric it will be absolutely fine, especially if no more than 2kg. This wall bracket takes an E27 lamp so your shade will need a larger diameter than a shade used for a B22 lamp.

Would this work with a glass shade? I'd like to use it with this one https://www.lightingstyles.co.uk/danish-compact-glass-and-metal-acorn-shade
Unfortunately I don't believe the glass shade would work with this long reach wall light. The arm is highly adjustable, as is the section which holds the shade, I don't feel it would look right (too small) nor be functional as intended.

When fitted to a ceiling, what is the minimum drop (without shade) and the maximum drop please?
The maximum drop is 800mm and 200mm minimum. There is a datasheet in the "more details" tab on the the page.

Is the length of the arm 800mm for both parts of arm in total ?
The reach of 800mm is the total span of the fitting.

I am looking at your long reach ceiling light ref 6782, because of it's flexibility of lighting options. Can I replace the shade with any standard shade of the correct size at my own cost to better suit my interior if I don't like the white or black shades?
Yes in theory you can use your own shades, but the shade you replace it with must weigh the same. Any added weight will add strain on the fitting joints.

Does this move left to right when it is wall mounted?
No unfortunately this fitting only goes up and down. The rotation only really works when it is ceiling mounted.