Hello there! I like the character! I understand that painting backgrounds can be challenging; it's not an easy task, haha. But remember that you don't always have to create everything from scratch. :) The main thing is to use references and avoid working purely from imagination, especially when a scene involves different light sources, such as interior scenes. Now, once you have your references, you have two options. One is to sketch everything from scratch using a single reference or combining different references. Alternatively, you can do a bit of photobashing. Take images with a simple perspective and adjust them to fit your character. From there, you can trace over the image and make adjustments to your liking. :) Ideally, avoid images with two-point perspective. Since we're viewing the character from the front, a scene with one vanishing point would be better. :) As for the lighting, look at references to understand how lighting works in interior scenes. In this case, since you mentioned that there will be several candles in the BG, you could keep the character in darker values and only paint the light coming from the sword, along with a rim light coming from the candles. However, as you can see in this example, I tried to adjust the character's lighting to match the lighting in the BG. :) Hope this helps!

Sometimes putting in a perspective grid will help suggest a background.