Recommendations for organising Catalogs

Until V7 I didn't use catalogs, but have been doing so for a while now. However I'm not sure if there are optimum ways to use them. For example, are there any negative aspects to having one large catalog for all my image files (around 500,000 in total) - would this give me best capability for searching metadata? Or is small best, so perhaps create one Catalog for each year (which would equate to around 30,000 RAW files).

Your suggestions would be appreciated on this.

Assuming I then re-organise my catalogs - at the moment I only have catalogs for either new photos I have taken since installing V7, or a mix of other catalogs for older files - Can I delele the catalogs but retain all the C1 settings generated in processing the files within them.

Neil