OP,
I was a Biology and Classics double concentrator at Brown and am currently a 6th year MD/PhD student. My course of study would not have been possible at schools with stronger curricular requirements.
With applying? Definitely the essay writing experience with the classics helped…not sure if I understand what you’re asking.
I don’t know how many schools actually have full undergraduate neuroscience majors. It will probably have less labs than engineering so I would put it on par with an arts and sciences major such as biology, biochemistry, chemistry.
Jug already talked about the gap year - it’s definitely easier to find a good gap year job than to get into medical school so if you can’t secure a gap year position you’ve probably got bigger problems. With regard to the MCAT, MCAT scores are valid for 3 years so by doing a gap year you can now take it at the end of the summer after your junior year (or later) rather than needing to take it no later than beginning of summer after junior year. Depending on your other commitments during the school year, having that summer to work on the MCAT can be a huge advantage.