Dim conn As New ADODB.Connection
conn.Open "driver={Microsoft ODBC for Oracle};" & _
    "server=js;" & _
    "uid=hsonschergffdg;pwd=xxdfhsons"
Set Cat = New ADOX.Catalog
Cat.ActiveConnection = conn
TotTab = Cat.Tables.Count

The issue here is
Surprisingly TotTab got a value much larger than what I was expecting.
The total number of user-defined tables & views are expected to be not more than 1500. But it shows some 8500 tables.

Is there any way to :
1) count the tables created by the users (all other system tables etc excluded)
2) when was a table last modified and by which user

1.) You can query the table USER_TABLES and get a count of distinct tables that are not system tables as follows:

select Count(Table_name) from user_tables;

2.) This is a function as to what is logged on your database or whether your tables have audit trail fields on them. This type of logging that you wish to implement is rather resource intensive. Typically, a database design that needed to keep track of such info might add fields to each record on the table that contained a transaction date/time, and userid. Then all you would have to do is query the table for the MAX value of date/time and you would have the most rcent update time and the user id who did it. Oracle does not automatically log such information.