For routes and inspiration have a look at www.crazyguyonabike.com there are loads of journals there.
I cycle a lot in Vn (about 4 months last year alone) and love it. Some find it too manic and the people too challenging, but I reckon it is a wonderful place to cycle once away from the big towns and the main north south Hifghway 1.
You need to be more specific with your plans before it is worth answering your post in any detail.
Wil you be taking a bike (local ones are usually pretty bad)?
How long cycling (days, weeks, months, etc)?
Daily distances?
Like mountains?
Like isolated rural areas or more touristy areas?
etc, etc?