design web app for my proj

My requirement is to create an application that sales plots to customer.

The customer may pay the amount for plot all at a time or in installments.

When The customer is new

1. Create the customer

2. Allot him a plot

3. Accept his first payment.

1Q. My question is do I need to create separate pages for the above operations?

When the customer is old

1. Just accept Installment Amount.

2Q.My question how do I divide the screen interface.

I have separate tables for

Customer

PlotSale

Payments

Hope I would be guided