re Ability to have field personnel use offline DBs, MySQL does not seem like the right candidate for this. Imagine, each field person would need mysql installed on their PC... which is not as simple as copying say a MS Access database file... and a 'custom' program would need to sync changes to the master database when online, etc. MySQL to my knowledge has not been used for this and has not been designed for this.
Try searching for crm in...
http://sourceforge.net
... for free / open source applications