Use your existing user table, and only import user_id in to blog_cat.cat = 1001 eg

REPLACE INTO blog_cat(cat,name,info) VALUES
(1001,'blog_staff','{"1":[1,2],"181130":[102,108]}');

staff user id is a json of: catetory and user ids, above means:

cat = 1 (all categories i.e. Admin staff)
user_id = 1, 2

cat = 181130 (i.e. staff or moderators for cat = 181130)
user_id = 102, 108 etc