I last flew Virgin LHR to MIA three years ago, so may be out of date here
(that's the disclaimer part over with!), but DH did it just last month, so I can check with him later
Food - had the lunch-first-then-ice-cream-then-tea-before-landing package that you get LGW / MCO.
Airport - can't remember the layout other than the lack of MCO double-baggage system! There's a Dollar desk inside the terminal and then all the rental shuttles are outside to take you to the various depots. When we rented with Dollar the shuttle bus was a complete bun fight and was the main thing that put me off MIA (temporarily

- we're planning this route later in the year), but DH went with Budget last month and had no problems getting that shuttle at all. I think you're using Hertz this time, aren't you? From Googling, I think the rental depots are all about a similar four or five minute bus ride from the airport.
Make sure you get decent directions BACK to the depot at the end of the trip, as it's not as easy to do as following the big airport 'rental return' signs!
BTW DH said there were some road works last month around the area between the airport and the Budget depot (so may not affect Hertz) that tested their navigational skills!