My guess is most of your meshes don’t have proper UVs for a light map, that’s why some things are black and you are getting errors and artifacts. UE4 automatically tries to create light map UVs for an asset based on the existing UVs, and you can view what it created by opening up the static mesh, clicking on the uv button and changing the uv channel drop down to UV Channel 1.
Also make sure when you are building you change the lighting quality to production (option is under build). The preview lighting renders leave a lot of artifacts, and as long as the level is small (and the lighting settings are reasonable) a production build doesn’t take long.
You could set up the scene for dynamic lighting, but for a simple interior scene, baked lighting is the way to go. You’ll get better results and less artifacts, but you do have to suffer through creating proper UVs that will work for light maps, and baking. Also you will need to set the light map resolution for each mesh, start small and work you way up, something like the tub should probably be 256, the floor and walls 512, the sink 128, etc. You can change your viewport from lit to light map density after baking to see if your light map resolution is reasonable.