1. You said that there is a white line on the inner wall of the mouth where the upper and lower rows of teeth meet (it does not protrude from the inner wall of the mouth). This white line is normal. As long as it is a normal occlusion relationship, there will basically be this white line on the buccal mucosa. Don't be careful, it's completely normal. Because the upper teeth are slightly outward than the lower teeth when biting, there will be a gap in this place, and the meat that has been in this gap will form traces over time, which is the white line you said.
2. Your wisdom teeth have not fully grown out, and the occlusal surface of your teeth covers your gums. Pay attention to oral hygiene at ordinary times, otherwise it will be easy to get inflamed if you are tired or your resistance drops. If it is often inflamed, I suggest you pull it out. Pulling out this tooth has no bad effect on your whole mouth, but it is good. After pulling out, it can eliminate inflammation and reduce oral odor.
3. It is normal for the gums of the lower teeth to be white, so don't care.
As for the occasional bleeding when brushing your teeth, I guess it is caused by soft dirt on your teeth. This way the brush can be clean. Brush your teeth up and down, not sideways. If there is still soft dirt or food between your teeth, you'd better floss it out. If you don't floss, use a toothpick.
I hope my answer is helpful to you. From the picture, your oral hygiene should be good as a whole. Keep it up. If you are worried, I suggest you go to a regular dental clinic or hospital for consultation.