I deleted some item files by hand, is that ok?
This is like editing a database with a binary editor and removing a few records by hand, it is not a good idea :-(
However, DNews is written for people just like you, the database will correct itself with a little luck. :-)
Please do not edit an item file and remove individual items or change them, this will corrupt the database and the items will simply disappear.
I deleted the history.dat file, is that ok?
No, it's not. You need to do this, type in:
tellnews rebuild_hist
And cross your fingers and wait until the rebuild finishes (it could take a few hours on a full feed system)