Thise's aat's one question. That's one question.

changed to one instead of "a" because your next sentence has another question

Thisere's a question. There's a question.

This would not normally be appropriate, but when someone is feeling contemplative, one might informally say something like "There's a question" for emphasis. (In this case, it emphasizes the "what have I done this year" question.)

Thiseat's a question. That's a question.

And a bigger question is what I should to do next year. A bigger question is what I should do next year.

And a bigger question is what I should to do next year. And a bigger question is what I should do next year.

And a bigger question is what I should to do next year. And a bigger question is what I should do next year.

Should + a verb, we don't use "to", for example: "I should eat something", "I should go home".

I have many things that I want to do and that I should to do, but some of them are very dependingent on the pandemic situation, for example, my travel plans. I have many things that I want to do and that I should do, but some of them are very dependent on the pandemic situation, for example, my travel plans.

I have many things that I want to do and I should to do, but some of them are very dependingent on the pandemic situation, for example,such as my travel plans. I have many things that I want to do and I should do, but some of them are very dependent on the pandemic situation, such as my travel plans.

I have many things that I want to do and that I should to do, but some of them are very dependingent on the pandemic situation, for example, my travel plans. I have many things that I want to do and that I should do, but some of them are very dependent on the pandemic situation, for example, my travel plans.

Same thing here, with "should", drop the "to" after it. Also, it is common to rewrite "that" after an "and" The phrase is "to be dependent on" or "to depend on". So you could either say, "some of them depend on the ..." or "some of them are dependent on the ..."

It'll be a new year afterin 5 days. It'll be a new year in 5 days.

It'll be a new year afterin 5 days. It'll be a new year in 5 days.

It'll be a new year afterin 5 days. It'll be a new year in 5 days.

When we are using a specific amount of time, we will use "in". For example: "In 5 minutes, the food will be done", "In 2 years, I will graduate", etc We use "after" with times if we are not using specific numbers, such as "After next week, it will be 2021", "After tomorrow, I go home to see my family"

I'm thinking about what I have donedid this year. I'm thinking about what I did this year.

"what I accomplished/achieved" would be better if you are talking about achievements instead of just normal day to day things

I'm thinking of what I have done this year. I'm thinking of what I have done this year.

I'm thinking about what I have done this year. I'm thinking about what I have done this year.

We often use the prepositions "of" or "about" with the verb "to think" think of = "想起来“ think about = “想某事“

I prefer to spend money on experiences, like travels, studies, and movies. I prefer to spend money on experiences, like travels, studies, and movies.

I prefer to spend money on experiences, like travels, studies,y, and movies. I prefer to spend money on experiences, like travel, study, and movies.

I prefer to spend money on experiences, like travels, studies, movies, etc. I prefer to spend money on experiences, like travels, studies, movies, etc.

You can either write "to spend" or "spending". If you don't use the "-ing" form of a verb, then you have to add the word "to" to the un-conjugated verb "experiences" needs to be plural here; I can't think of the rule, but if it's singular here, it sounds like work experience (简历）rather than having fun. Adding "etc" is not required, but it sounds better. Usually in English, when we write a list, we can either use "and" with the last one on the list, or use "etc" (等等）