If you are a university student living alone, I want to ask you,: does your room have enough space? If you are a university student living alone, I want to ask you: does your room have enough space?

If you are a university student living alone, I want to ask you, does your room have enough space? If you are a university student living alone, I want to ask, does your room have enough space?

Ask "you" is implied here because you've already addressed the reader earlier in the sentence, and the question is also phrased about "your room", so it's a little more natural to omit the extra "you" here

One of my friends, who comes from the countryside in northeastern Japan, is now living in Tokyo to attend university there. One of my friends, who comes from the countryside in northeastern Japan, is now living in Tokyo to attend university there.

One of my friends, who comes from the countryside in northeast Japan, is now living in Tokyo to attend university there. One of my friends, who comes from the countryside in northeast Japan, is now living in Tokyo to attend university there.

When I opened the door, there iwas a kitchen in the corridor. When I opened the door, there was a kitchen in the corridor.

This should be in past tense since you're talking about something that happened.

When I opened the door, there is aI noticed that the kitchen was in the corridor. When I opened the door, I noticed that the kitchen was in the corridor.

When I open the door, immediately there is a kitchen in the corridor. When I open the door, immediately there is a kitchen in the corridor.

"immediately" is like まっすぐに. It helps emphasize the fact that you were surprised by the immediate position of the kitchen. 「Immediately」の言葉は「キッチンの位置はびっくりしている」の意味を示す言葉です。

When I opened the door, there iwas a kitchen in the corridor. When I opened the door, there was a kitchen in the corridor.

She hasd only one living room in which there arewas a desk, a bed, and some musical instruments. She had only one living room in which there was a desk, a bed, and some musical instruments.

See above for note on tense.

She has only had one living room in, which there arehad a desk, a bed, and some musical instruments. She only had one living room, which had a desk, a bed, and some musical instruments.

She has only one living room in which there areis a desk, a bed, and some musical instruments. She has only one living room in which there is a desk, a bed, and some musical instruments.

The particle you use should reflect the first item in the list, and since "desk" is singular, you should use "is". An example when you could use "are" is this: "There are markers, a highlighter, and a pen on the desk".

She has only one living room in which there areis a desk, a bed, and some musical instruments. She has only one living room in which there is a desk, a bed, and some musical instruments.

I had to sleep atin the space between athe desk and athe bed. I had to sleep in the space between the desk and the bed.

Since you've specified that there is one desk and one bed in the room, here you should use "the" to refer to them instead of "a".

I had to sleep atin the space between athe desk and athe bed. I had to sleep in the space between the desk and the bed.

I had to sleep atin the space between athe desk and athe bed. I had to sleep in the space between the desk and the bed.

"In" emphasizes the location where you are sleeping. "At" is more broad and not really used alongside "to sleep". Make sure to use "the" rather than "a" when you want to discuss a specific desk and specific bed. This is the desk and bed is not random, but your friend's, so you should use "the desk and the bed" to emphasize that unique situation.