1. Cardinality Based Analysis
2. Query Decomposition and Reconstruction

1. you have smartly used the WITH clause here to incrementally build your query.  This is very good.  And it will also make it easier for you to do the process of decomposition and reconstruction.  I note that there are several independent sub-queries in this large query.  You should use create table commands to materialize each of these sub-queries.  This will allow you to see how long the sub-queries take on their own which may lead you to one of them taking way too long and thus possibly being your problem, which you can then fix.  And they will allow you to compare row counts from each query plan step to see that they match expectations.

2. the query makes use of a remote query or object.  You should materialize that object or query locally and then run tests and do the decomposition and reconstruction process using this local copy, in order to learn how much time is related to working with this remote object.  This will give you an idea of how much the remote-ness of the query is contributing to overall runtime and thus, if part of the problem, will lead you in the right direction for solutions.

3. once you have all the independent parts, you can materialize the main query using the tables your created for the sub-queries.  This will tell you how long the joining etc. of the main query is taking.  This you can do one table at a time as is described in one of the attachments.  Again this will show you where your time is going and thus where maybe there will be a potential fix.

4. I note that you have some user-defined functions as well.  It may be that these are part of your problem.  Since it appears these only show up in the main query, these can easily be evaluated by simply removing them from the query to see if it runs a lot faster.

5. also, there is a SCALAR SUB-QUERY in your query.  This too my be inefficient which you should check. If it is actually being done (it may not be (see notes below)) then it could be a cause of performance pain.

Lastly I note that the query contains something like 30 table references yet the query plan you provided only shows 8 or so.  So either the query plan you have given us is not the plan for this query, or we see in this query plan, the magic of Oracle's optimization which I call DUNSEL JOIN REMOVAL and which Oracle refers to as JOIN ELIMINATION.  The CBO has determined (likely due to the outer joins in this query) that most of the joins it is doing are not needed because they neither change the number of rows in the result set, nor provide access to data needed by the result set, and thus the CBO has removed them from your query.  You should validate that the plan you have shown us is in fact the plan that has been used to execute with.  If Oracle is using this query plan, it has already saved you possibly hours of runtime because of this optimization (what a smart database we have).