"I cannot go because I do not have a visa."
我不能去因为没有签证。 Should be accepted answer. I believe mandarin sentences doesn't require one to repeat the subject
It's not necessary but it is added so the sentence sounds smoother （比较顺）, which is important in choice and order of characters, or when choosing which of several acceptable sentence structures is "best".
I also wrote this because it is the sentence structure taught in an earlier lesson.
I believe 因为我没有签证我不能去 should be accepted. This is in line with the form 因为 ... 所以which is typically how Chinese express cant do something because. Interested to hear from native speakers
I don't think so. There are three patterns that we should stick to:
Effect, 因为 + Cause
Cause, 所以 + Effect
因为 + Cause, 所以 + Effect
If you want to put Cause part first, then you cannot skip "所以" before Effect.
I started with 应为我没有… because that's the word order taught in all the previous lessons; at least it's good to know we can reverse the clauses.