Trains run about every half hour. The MARC line schedule is here (https://www.mta.maryland.gov/schedule/timetable/Marc-Penn) and should cost around $7-10. Amtrak runs less frequently but has bigger seats, should cost about twice that $14-20ish Ride lasts anywhere from 30mins to an hour depending on which train and how many stops. Not a bad ride.
Yes, review both MARC and Amtrak to see which best suits your requirements.
Yes, you can take the MARC or Amtrak. The trains are plentyful. Amtrak is a little more expensive. Don't know pricing
Yes. MARC train is the local service, it's about $7. Amtrak is the other option. It will be considerably more expensive.
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