These are fairly OK starts. I ran an environment design course here under my named account a while ago. This video is a demo of the value blockout stage (though for an imaginative piece) .
https://youtu.be/E9zy0OOpT9o
Added some textures at the end which may help you around 31 mins (not much but a brief technique is shown there)
Main thing with these studies is to really hone your sense of shape/composition/value hierarchy and depth. Make sure these are as accurate as possible first and read well. That will give you the biggest return. There is a thread here called Environment Design Rocks in the mentor section. It has a ton of student work in it. Maybe some will help you
Before texture, pay attention to edges. Edges are generally broken down into hard, firm, soft and lost. Photographs tend to make many things harder edged and detailed than you would observe from life. If you want to paint realistically the magic is heavily dependent on the balance of edges. Squinting your eyes reduces the edges you see to only the hardest the more you squint. Use that to identify which edges to keep hard. Note this is mostly when drawing from life.
Digitally, texture can be painted individually with a smaller brush it just takes longer. It's far more efficient to use a textural brush and experiment with what works for the effect you're trying to achieve but the downside there is you will need experience to get this to work well right away so be patient. Chalk brushes tend to be generically useful but any can work. If you clip the texture layers as new layers and erase /smudge you can manipulate your texture painting easily by painting and erasing and not worry about breaking already described shapes. A simplification strategy to use can be that in directly lit situations (clear cast shadows) textural information is most visible at the place where the lit areas meet the core or terminator shadows. A bit of texture In that transition area can go a long way towards describing the entire form as our brains fill in the rest. Err on the side of implying detail not adding it everywhere.
My advice is aim for accuracy first in overall read of your studies and this is mainly done with proper value arrangement and accuracy of the simplified but accurate shapes and atmosphere. The rest is incrementally adding detail.
Do more. Nail the read of the image first. If it isn't recognisable without the reference it likely isn't a good study
