How to optimize this dynamic stored procedure

I have a stored procedure which is retrieving data using 20 tables. Sample of the procedure:

     CREATE PROCEDURE GetEnquiries 
     (
        @EnquiryDate    DATETIME     = NULL
     )
     AS

     DECLARE @querySELECT      VARCHAR(MAX) = ''
     DECLARE @queryWHERE         VARCHAR(MAX) = ''
     DECLARE @queryExtraColumns     VARCHAR(MAX) = ''
     DECLARE @queryReturnResults    VARCHAR(MAX) = ''

     -----------------------------------------------------
     --Create temp table
     -----------------------------------------------------
     SET    @querySELECT = '
             CREATE   TABLE #tempResults 
             (    
              EnquiryId     INT, 
              Cost         Decimal(18,2),
              CustomerName    VARCHAR(50),
              EnquiryStatus   VARCHAR(50),
              ContactNumber   VARCHAR(50),
              NumberOfVisits  INT 
             ) '

     -----------------------------------------------------
     --Insert into temp table
     -----------------------------------------------------  
     SET    @querySELECT = '      
             INSERT INTO #tempResults 
             (    
              EnquiryId     , 
              Cost         ,
              CustomerName    ,
              EnquiryStatus   ,
              ContactNumber   
             ) '
     -----------------------------------------------------
     --SELECT
     -----------------------------------------------------
     SET    @querySELECT = '
           SELECT         
              e.EnquiryId     , 
              e.Cost       ,
              c.CustomerName  ,
              e.EnquiryStatus ,
              c.ContactNumber 
           FROM  Enquiry e
              INNER JOIN Customers c ON e.CustomerId = c.CustomerId '

     -----------------------------------------------------
     -- WHERE 
     -----------------------------------------------------
     IF(@EnquiryDate IS NOT NULL)
        BEGIN
           SET @queryWHERE = @queryWHERE + ' CONVERT(VARCHAR(10),e.EnquiryDate,23) >= '  + ''''+ CONVERT(VARCHAR(10),@EnquiryDate,23) + ''''
        END

     --- There are at least 14 parameters used in WHERE operation the above is just one of them
     -----------------------------------------------------
     -- Count NumberOfVisits
     -----------------------------------------------------
      SET   @queryExtraColumns = '
           ;WITH NumberOfVisits AS
           (
             SELECT  t.EnquiryId, COUNT(EnquiryId) AS NumberOfVisits 
             FROM NumberOfVisits v 
                  INNER JOIN #tempResults t ON v.EnquiryId = t.EnquiryId
             GROUP   BY t.EnquiryId
           ) 


       UPDATE    #tempResults
       SET     NumberOfVisits = u.NumberOfVisits
       FROM  #tempResults t
          INNER JOIN NumberOfVisits u ON u.EnquiryId = t.EnquiryId

'

     -----------------------------------------------------
     -- return the results
     -----------------------------------------------------   
     SET    @queryReturnResults = '
           SELECT         
              EnquiryId     , 
              Cost         ,
              CustomerName    ,
              EnquiryStatus   ,
              ContactNumber   ,
              NumberOfVisits
           FROM  #tempResults t 
               '

     -----------------------------------------------------
     -- Combine all the strings + DROP the temp table
     -----------------------------------------------------  
     -- PRINT(  @querySELECT + ' WHERE ' +   @queryWHERE + @queryExtraColumns +   @queryReturnResults + '  DROP TABLE #tempResults ') 
      EXEC( @querySELECT + ' WHERE ' +  @queryWHERE + @queryExtraColumns +  @queryReturnResults + '  DROP TABLE #tempResults ') 

Some facts:

• The above procedure is the simple form of the Stored procedure i am working on.

• I am using SQL Server 2008

• My Actual procedure has 15 parameters, all of them are used in WHERE clause. If the value is provided for a parameter, the parameter is included in the WHERE clause otherwise not.

• There are at least 10 columns whos value comes from the GROUP BY condition like the one "NumberOfVisits" given in the above procedure.

• I have indexes on all the Primary Keys & Foreign Keys.

• I have indexes on all the columns that are used in the WHERE clause.

• I have indexes on all the columns that are used in the GROUP BY clause.

Questions:

• Is this is according to the best practice to create dynamic stored procedures following above pattern?

• I got the output SQL of this procedure by using: -- PRINT( @querySELECT + ' WHERE ' + @queryWHERE + @queryExtraColumns + @queryReturnResults + ' DROP TABLE #tempResults ') when i run that SQL it took the same time that was taken by the stored procedure, why? is the SQL should take less time?

• Is the above is the best practice to get the value of summary columns("NumberOfVisits") ?

• is the above is the best way to create the WHERE clause dynamically?

• Can i avoid the use of Temporary table by using some alternate in the above scenario?

• What can i do to optimize this procedure?

Please forgive me, if my question is NOT clear or not a proper question.

Thanks for your valuable time & help.