Recommended partition size MacBook Pro (Mavericks) for Windows 8.1, Windows database app? Any suggestion regarding size of partition to set in Boot Camp to be sure of having adequate space for Windows 8.1 and at least one large Windows application, a custom database application?  I'm thinking about 150 GB ...
Windows 8.1 takes 20GB (16GB for x86), a database application like MSSQLS takes 1-5 GB depending on the features you install.  A database with 10,000,000 entries is roughly 1-10 GB.

150 GB is a lot, IMHO, but it depends what else you want to do with it and how much memory you have available of course.