Big layouts are generally fine. I've seen games using layouts much larger than what you're wanting to use - with no problem.
My "map" for my game is totally unbounded layout - it goes literally forever. No issues.
The thing to watch out for is really the number of objects that are actually on screen at once, and things like collision checks, loops, and object placements - if you have a lot of objects in your layout you will need to make sure you're not checking for things that don't need to be checked for (like anything that isn't on screen at the time can have collisions turned off, etc).