Need better at understanding on the implement Pattern and Better Code

hi,

Almost all of the programs that I have made no use pattern (still using raw.ado), I get a lot of problems when a client asked me to replace the database.
I have read the code in the sample Patterns In Action, there I have some questions :
1. If I make an application, my example inventory application (Item, Supplier, Customer, Order, Invoice, etc) 
Should the application that I have to apply more than one type of pattern ? I note that, in the Pattern In Action example uses a lot of pattern (MVC, Factory, etc)
2. Where i can find examples input of master-detail data ? (Invoice, Detail)
3. I am currently separate project by module (1 Solution (Inventory),  has several projects in it that represent each module)
this model can also be applied Pattern ? (include Image)

Regards,
Eric Santoso