hi,
* start with a nav cronus database
* then check how to work with nav
* then best buy a nav dev. book (mark brummel, ...)
* then import your customer/vendor/item data step by step following
msdn.microsoft.com/.../hh179459(v=nav.70).aspx
msdn.microsoft.com/.../dn848428.aspx
* then design the needed reports
* so, set up your nav environment step by step, work with the current nav database
* and change the system and the data only if needed
* it will last some time, but it is possible
* ... and ... it is ok to make failures.