So I have another question, my client is entering invoices for their clients with an invoice date in the future...03/03/2012 for a payment which is a payment plan of monthly installments. Now will an email go out automatically on 03/03/2012?
No.
and how to set up an "upcoming payment" reminder email to go about about 3 days before the due date or invoice date?
You can use an 'invoice overdue' reminder, but change 'send after' from 'yes' to 'no', and change the default wording of the reminder message.
Also, in this sceniro are future invoice dates treated as due payments?
There isn't really a concept of 'due payments' in nBill, other than orders with a 'next due date'.
Also, once this client pays this invoice let say for $250.00 on a loan of $7,000 with monthly payments of $250.00, does a new invoice need to be created for the April payment and is there a better solution to automate this?
No, where a payment plan is assigned to an invoice, and the payment plan stipulates monthly payments, when the client goes to pay the invoice, it will attempt to set up a recurring payment schedule to automatically take the installments each month (subject to the payment gateway supporting this). For example, with Paypal, this will set up a Paypal subscription which expires once the full amount is paid. Each payment is marked off against the original invoice, so there is no need to create a new invoice each time. The invoice will be 'partially paid' while the installments are coming in, and will be marked as 'paid in full' once the full amount of the invoice has been paid.