Here are some quick tips for future levels based on some stuff I saw in the map:
- Right now your room looks like "a box with stuff in it". Try to work on making an area seem more natural-shaped instead of specifically square, as though it's "a place that exists" as much as it is just a level. Slopes can really help with helping an area feel organic and natural if you want to try using those. They're an in-map linedef effect that you don't need control sectors for and are pretty easy to set up. Try opening up an existing map and looking at how they're used, if that helps.
- When placing rings, it's best to keep them in separate rows of 3-5 for most occasions. Ring lines can help guide the player in the direction you want them to go or to points of interest in the map, but shouldn't be relied on exclusively.
- I'm not sure what the sector around the edge of the map is supposed to be - are you trying to create a thok barrier? We don't really need them except for visual purposes anymore so I would just ignore them until you need a way to place two separate textures on a wall or allow the player to see the sky.
- If you're in 3D mode, you can autoalign textures like the stairs with the A key (I think that's the default key? Correct me if I'm wrong) - by default it aligns all adjacent linedefs that share the texture you point at, but you can select individual linedefs and have it align only those and not other ones.
- Don't be afraid to make sweeping changes like cutting the room in half and making one half way taller than the other half while you're experimenting! It's important that you figure out ways for the player to get to cool places, and to make those places look cool.
- Colormaps are a linedef effect, not a sector effect - you want to give the water's control sector a tag, then have the colormap linedef share that tag for it to work. You also need to write the colour code in the upper texture field of the colormap linedef (eg. #0000FFJ used to be the standard water colormap in 1.09.4.)
- Try not to make sectors brightness 255 unless they're literally a source of light, or darker than 160 except for maybe water control sectors or lighting in pits. The brightest of outdoor areas should be 240. The way that Software handles lighting, having an area be 240 brightness or lower allows for players to have a better sense of depth and how far away different points in the level are. It subtly helps with platforming and a lot of other aspects of the player finding their way around.
- The wiki is your best friend if you ever need to reference how to set something up, or how something works! Check it if you have any specific questions, and it might answer them for you.