I'm converting an 80 year old detached garage into an efficiency apt. it's approximately 400 sq. ft. 11 ft. ceiling. It will be basically one big room plus bathroom. This is in South Florida with high humidity and I have been told that an over capacity a/c unit may not cycle often enough to remove the moisture in the air. The location of the unit will be wall mounted at a centerline height of 8'. I ran two separate cables to this spot so I can utilize either 110V 20AMP or 220 30 AMP .What would you recommend as to: BTU capacity, 110 vs. 220, or other factors I should consider? Thank you

You really need to do a manual J. Window size and type along with wall and floor construction are just a few things to consider when size is a concern. 120/240 no difference with a unit that will be so small.

Just a guess

8,000 to 12,000 BTU mounted midway up wall with discharge air vanes pointed towards ceiling allowing the cold air to drift down. Smaller is better for humidity removal. The right size unit will run 20 out of 24 hours per day and act like a big dehumidifier.