That will be up to your vet. I would schedule an examination. Record his weight. Have the vet compare it to previous weight's. If holding steady, that is a positive indicator.
Next, the vet should assign him a body condition score (BCS). This helps a vet to determine if they are an ideal weight based on their confirmation, or if they appear over or under.
Lots of pets are always looking for food, and obesity is a horrible problem in veterinary medicine.
So, have your vet evaluate him first to see his weight trends and if his body condition is adequate.
This changes your initial question A LOT.
Yes, a barium study would be helpful to assess for motility disorders of the esophagus, lower esophageal sphincter problems, and for megaesophagus (a dilated esophagus). Scoping (endoscopy) could also be helpful.
Helpful medications to discuss with your doctor includes metoclopramide or cisapride, which are motility enhances to help empty the stomach quicker.
Also, feed from an elevated food and water bowl.
Well a dilated esophagus allows food contents to sit longer in the esophagus. bad.
This is very different than an actual motility disorder. They need to see how much barium makes it to the stomach, or is it being regurgitated in the esophagus. If it never makes it to the stomach, the cisapride may not be helpful.
Definitely, barium is a good next step.
Sorry, that I can't answer. They are two different conditions, and I really can't even account for the finding of a "small area" of dilation. Generally, a megaesophagus can be seen clearly on an x-ray. The barium is to diagnosis a motility disorder. In a way, a megaesophagus could be grouped into motility disorders.