The most natural way to say this is, "the place that I want to go to most." You would use both because in the first case it is a verb and in the second case it is a preposition. So it is the same word serving two different purposes. To answer the second question, your sentence is grammatically correct and can be left as it is. You are correct in your thinking that the conjunction serves the purpose to connect the subject to the verbs in both halves of the sentence. If someone is telling you to put "they" in there, it is because they would say it like this, not because it is wrong without it. The way people speak in America is different from other English speaking countries and even within America, people speak differently according to the area of the country where they live, their education, and sometimes economic background. So what is natural for one person may not be natural for another. Take that into consideration when you read these answers.

1. You could say both and I can understand. Perhaps, If you want the most natural way combine (to like a place the most). I would say this: My favorite place to go. (If I had been there before) Or perhaps, The first place I would like to visit. (I had never been there before) 2. The second sentence needs a pronoun or noun to specify who is doing the action of the verb since in the previous sentence you used a decriptive verb. It only works if they are both the same type of verb. For example, you can say: I am tall and wide. you can say :I went to the store and ran home. You can't say: I ran home and tall. You can say: I am tall, and I ran home

In English generally we always have to state the pronoun for it to be grammatically correct. Someone would understand you but likely correct you as it doesn't sound right. If you were to say "The crew members go on a trip together" "they" is not necessary because "who" is stated right before what they are doing. I hope this helps. If not let me know and I will try to explain a little better.