How detailed should my books be?

[Richard Arden]

I use Stessa and was wondering how detailed I should be when it comes down to filling my receipts.

I only own one duplex and I have been recording things as simply as possibly. Should I be breaking down costs in Stessa?

For example.

Should I split up my mortgage payment into each of its parts principle, interest, taxes, etc. or since it is one bill leave it as such?

When I buy a maintenance item that will be used for both units at one trip to Lowes should that be divided down?  

When I refinanced my mortgage should I have split up all of the closing costs into different categories?