SQL & PL/SQL :: How To Combine Queries When WITH Clause Is Used

I have 4 select queries.

Query1
Query2
Query3
Query4

First Step:Combine Query1 and Query2,but the requirement is Query2 should only use the Acct_ID and Bill_ID which are output from Query1.

Second Step:Combine Query3 and Query4,but the requirement is Query4 should only use the Acct_ID and Bill_ID which are output from Query3.

Third Step: Is to now combine both the data set from First Step and Second Step.

In order to achieve my First and Second Steps I used WITH clause.

With S1 as ( Query1 ),
S2 as ( Query1 Union Query2)
Select S2.* from S1,S2
where S1.ACCT_ID=S2.ACCT_ID
AND S1.BILL_ID=S2.BILL_ID

With S3 as ( Query3 ),
S4 as ( Query3 Union Query4)
Select S2.* from S3,S4
where S3.ACCT_ID=S4.ACCT_ID
AND S3.BILL_ID=S4.BILL_ID

1. Is that approach right for achieving my First and Second step requirements ?

2. How to achieve Third Step ?