I'm sorry to dissapoint you, but you spoke to tier 1 agent who likely didn't know what's going on with your case. They're likely gave you a satisfactory response to get you off the chat and serve the next person. Do not buy into what they said to you. Majority of cases go through "being actively reviewed by USCIS", before switching to other status. Usually it doesn't mean much, as people see this status for weeks or months. Another infamous status is "Interview is ready to be scheduled". Some people see it for up to a year.
1. It's totally fine you haven't received the letter, usually it takes 2-6 weeks after filing.
2. You cannot be sure whether biometrics will be reused. You may be invited for appointment, watch out for a letter and case status. It may take up to 6 months after filing to receive it!
3. It's very undesirable to miss biometrics appointment if you get it while abroad. Your case may be denied because of missing it.
4. Don't travel overseas without GC + extension letter or ADIT (I-551) stamp in passport.
Good luck!