Le sigh. The number of seats that you supply in a route does not impact how many tickets to you will sell. Please note I'm not refering to load factor, but seats sold. Load factor is a calculation of seats sold divided by seats available and is not a good metric for determining what you want to do. Second, RI does not increase faster with multiple flights per day.
So, to answer the question, on a 1000 demand route, when you start it with an ri of 0, you will be able to sell 200-300 tickets at the very most. Therefore, if you supply 250, you'll have full planes within a week or two of starting the flights. However, if you supply 500 seats, you will still sell the same number of tickets and have half your seats empty.