Maine coons do need regular brushing to avoid mats. They can mat very quickly, if they do its best to cut them out carefully instead of tugging at their skin. Brushing once or twice a week is recommended.
Its best to offer fresh water at all times. I leave out dry food at all times and offer wet food twice a day. Upon pick up I share my homemade recipe that you are welcome to use if you have the time and resources.
You should set up a vet to do regular check ups and have available if needed. They will be microchipped, have at least one vaccination (we start them late to avoid reactions), and they will come with these records. If they have parasites we treat, but do not treat unless needed.
Maine coons take a bit longer in most cases to adapt to new homes. Expect them to hide the first three days, give them a quiet room where they can learn sounds and smells of their new home and venture out on their own.