Need a suggestion for Database Design

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SQL-Server

Oracle

Hi fellows hope so all are doing good :)
      I am developing a Sale/Purchase system for a local store where data may varies from thousands to about a million of records. I need two suggestion for database design.

1. Question 1)
   
   
   
   • In my case there are two types of Clients "Individual and Company".
   • Company can have more than one Representatives and have more properties(Columns) than Individuals
   • So I creates two tables in parent child combination. Clients with some properties and Companies with extended properties
   • A Bill will be generate against a Client
   • Every entry of type Company, Individual and Representative will go in Clients but only Company type Client will be inserted in Companies(Extended) table
   • Companies have 5 or 6 additional columns except Client_ID(FK from Clients table).
   • I put companies and individual clients together because there are some common columns like balance, credit limit, member package, account info(There/His bank accounts we are dealing with) e.t.c
   
   So what if I merge both tables. Would saving 6 bytes per record is better or eliminating a table or join.
   
2. Question 2)
   
   
   
   • I have to manage balances in two tables 1. In Clients 2. In Accounts
   • And for sure each table have a column named Balance with type money
   • Account table holds information about Bank/Cash in hand accounts of user not the balance of a client. Client's balance is in Balance column in Clients table for which I am asking to split or not.
   • I heard that frequent update of a record(column/like Balance in this case) effect the performance of queries even of select
   • And I heard it too to keeping frequently changing columns in smaller table other than larger table can give better performance I don't know is this write or not :(
   • So if the above statement is true than what if I create a table of Balances with auto incremental ID and make it's reference to both Clients and Accounts tables. One to One relation
   • I think it will increase the update performance for Balance but will increase an inner join for SELECT
   
   


Thanks in advance and I am sorry if a have make any blunder :|