How many users are on list xxx

To determine how many users are subscribed to a particular list, simply query the members_ table:

select count(*) from members_ where list_ = 'jazztalk' and MemberType_ = 'normal'

If you want to know the breakdown of members by type, on a list:

select MemberType_, count(*) from members_ where list_ = 'jazztalk' group by MemberType_