Well, no one can answer this as this involves so many factors like routine/non-routine application, LVO, additional security/residency checks and many others. You can look at the 2019 and 2020 Citizenship applicants in my signature and look at the timelines yourself. There is no standard timeline, it is very erratic. If you are a 2020 applicant, to avoid disappointment, assume it'll take 18 months or more. If it comes sooner, that's good.
Well, yes. There are some people who get an interview after the test to verify stamps on passport. Again, depends on the case and the officer processing it.