Not a teacher, not a native
1. It is grammar mistake and not grammatical mistake.
2. I would use "on the street".
3. "Invite" does not require an in: invite
4, The tenses are fine. was/were chatty: they both work. I agree with the punctuation.
5. The second sentence is perfect.
You may want to read this:
The use of past perfect in before-clauses is actually quite common. The use of the tenses in such patterns is perplexing because it appears to be a violation of what is normally advised, namely: The action which occurs previously in time is expressed in the past perfect tense, and the action which occurs later in time is expressed in the past tense. This normal situation is shown below. Note how both actions actually took place. The letter really was written and the letter really was mailed.
Student or Learner