setting up business contacts

I am new to BCM. Am uploading business contacts from several sources. So
far I have uploaded two lists and have differentiated them by using the
source field. One list comes from a vehicle registration list and the other
from our in-house Sales Manager who has contacts he currently targets. I
have two questions:

1. How do I merge the duplicates into one record (they won't have the same
info., so I will need some info. from one list and some from another, ie. the
Sales Manager list may be missing data that the registration list has
complete. Conversely, the Sales Manager list will have info, ie. cell phone
# that the registration list doesn't have).
2. If this has to be done manually, so be it, but it then brings up another
question. Let's say I have brought in 4 different lists and now have 300
contacts. Can I assign multiple categories (category may not be the right
word) to individual accounts. Let's say contact number one should be on a
list for mailing a and b, while contact number two should be on a list for
mailing b, c and e? I see how accounts can be categorized, but I don't see
how an individual account can have multiple categories.

Any help would be greatly appreciated.
--
Julie