Take the school's placement test, which is usually free and takes part of a morning. It normally has a written section and a short conversation, because people are rarely at the same level in both. Do not talk your way into a higher class than the test suggests. Being the weakest person in a room where you understand nothing is the fastest way to stop attending.

Only if you actually need the certificate for a university place, a job or an application. Exam courses spend a lot of their time on question types and timing, which is useful for the test and less useful for talking to a landlord. If nobody is asking you for a score, a general class will improve your English faster.

Generally yes, because a room where nobody shares a first language has to use English to get through the hour. A class where most students share one language slips back into it the moment the teacher turns around. That said, a teacher who speaks your language can explain a grammar point in seconds that would otherwise take a lesson. Ask what the mix usually looks like.

A recognized teaching certificate for adult English learners, not simply a degree and a native accent. Ask what the teachers hold and how long they have taught. Being a fluent speaker does not tell you how to explain the present perfect to somebody whose language has no equivalent, and that is the actual job.

Conversation clubs at libraries, faith groups and community centers, language exchange meetups, and volunteering somewhere that forces you to talk to strangers. Classroom hours alone are rarely enough to build speaking confidence. Ask the school what it runs outside lesson time, because a school with a social program is handing you the hours you need free.

Schools and districts usually provide language support for school-age children, and private schools run separate junior classes rather than seating a teenager with adults. If a young person will be in an adult evening class, ask how that is supervised and what screening the school runs on staff, since the rules for adults working with minors are set state by state.