How accurate is the transcribe pass?
On clean dialogue it is close, and it is usually faster to correct than to type from scratch. Plan on a correction pass for names, jargon and overlapping speech: it is a draft, not a transcript.
Can I import an existing SRT file?
Yes: standard SRT files load onto the subtitle track, which is the easy way to bring captions from another editor or a client. Export works the same way for handing captions back out.
Should captions be burned in or delivered as a file?
Burn-in for vertical social, where the look is part of the design and the platform will not offer its own. An SRT sidecar for YouTube and anywhere accessibility or translation matters; keep the master clean for both.
Do captions help reach, or only accessibility?
Both. A large share of feeds are watched muted, so captions carry the story on their own; platforms also index the text in sidecar files, which quietly helps discovery.