- 저는 미국에 갈 거예요 = I will be going to the US / I will go to the US. (expression of a will or a half baked plan). - 저는 미국에 갈 에 가요 (incorrect) => 저는 미국에 가요 = I am going to the US (almost a certainty, or already starting). And yes, there should be a space between 에 and 가요. 에 is like "to", and 가요 is a verb, so they cannot be written without a space.

“저는 미국에 갈 거예요” is “I will go to US” Also you can switch “will go” to “am going to go”. The second sentence is not correct. Because 갈 and 가(요) mean both of “go”. But you can say like “저는 미국에 가요”. It means “I am going US”.