Seems like things are coming on nicely with your renders. I have also struggled with finding tutorials and information regarding specific ways of doing things in Maxwell over the years. Personally I don't mind youtube videos if they are informative and get to the point! I have a 2 monitor setup, so it is slightly easier to follow along.
When I first started rendering with Mental Ray way back in 2005, I spent a looong time searching for the magic render button/setting that obviously didn't exist! It took me a while to realise that even though my lighting setup was OK, the textures I used were just not good enough. Once I started using 4k textures for the major elements in my scene, as well as decent roughness and normal maps (instead of bump maps), my renders started to improve greatly. 8K textures are still a bit overkill for most things, although I am starting to use these more and more, especially for larger areas, such as floors etc.
I then realised that whilst my textures looked really good, the models I used really lacked detail and detracted from the realism I was trying to achieve. I invested in detailed 3D models such as from Evermotion, Bentanji (have a lot of Maxwell ready models), CGMood (3 free models/day to download), CGTrader etc. Of course a lot of these sites are paid models only, and if you are doing this as a personal thing, then perhaps it is not economical, although there are other sites offering free resources.
You have made a lot of improvements in your last image, especially with the towels and wooden bench. The tiled floor looks to have a nice, subtle amount of roughness to it that is indicative of a non-slip floor. I think the wooden walls could do with a bit more grain strength in the normal/bump map- Nothing much, just something to slightly catch the light. At the moment it looks a bit flat and smooth. Given that is such a large part of your scene, tweaking that material alone will enhance the image.
I found this interesting article on the Poliigon website blog that might be of interest to you regarding interior lighting tips. https://www.blog.poliigon.com/blog/7-mi ... ng-archviz
Don't be afraid to experiment with additional lights behind the camera, even though they may not be anything there in the scene.... Architectural photographers spend a long time setting up interior photos with extra lights and can be a great way to highlight individual objects if doing a close-up shot for example.