"Best practices" suggestions?

I want to start using MrProject for my scheduling needs, but I'm a little
unclear about how to start.  For example, I'm an independent contractor, so
I have quite a few clients, and I'm not sure whether I should be shoehorning
all of the tasks into one big project file, or trying to coordinate them
across several smaller ones.

General:

  Is it possible to give a set of default values system-wide?  For example,
I'll also have the same resources available - namely, me and a couple of
subcontractors.

Time:

  Is it possible to give projects a default time resolution of less than 1
day?  Many of my tasks are in 15- or 30-minute blocks.  Can I configure
MrProject to not display overnight hours by default?

Cost:

  How do you assign a cost to a task?


In short, I know that this is a really flexible app, which can be a
double-edged sword for new users.  :)
-- 
Kirk Strauser
In Googlis non est, ergo non est.