32-bit or 64-bit for development and deployment?
If you distribute your application with scripts to build the database (not a database backup or something like that), then in theory it should make no difference which version (of 32-bit and 64-bit) you develop against. Back when 64-bit was new and shiny (which was SQL Server 2000), there were some advanced features that 64-bit didn't support, but in 2005/2008 they should be functionally identical.

(Not that it should matter if you're using Compact Edition, but there are some configuration differences between 32-bit and 64-bit once you get to the point where your DB performance is an issue.)