Excel Macro

I require an Excel Databasing building which includes Macro's which allows for me to 'EASILY' input new customers to the excel database which captures customer information when they make a purchase from us, when creating a new customer it should populate a 'Unique' ID number following a pattern (e.g ER-0001, ER-0003). I also want an additional Macro TAB which allows us to 'SEARCH' for exisiting clients. Along with another TAB which shows summary of the database, such as number of customers.
I started a project on here which somebody started to create and send some examples which I like, I have attached these which you can copy/tweak. Which should save you some time.

I am not interesting in tracking payments, missed payments or stock control, as I use an alternative software for this, however I do want to see a summary off all my customers and when the 'Break Even' date would be. I imagine I would need to enter the cost price etc when inputting a new customer?

Other things to take into account are;
How would I add an extra week to the contract if a customer misses a payment.
I want to projected payments incoming via calander month.
Also a collumn to add notes per customer.

About us:
We are a small rental company who provides electronics equipment (TV's Washers) on a 'Pay Weekly' scheme, I want a database to capture all my contracts.

The information I want to capture is:
Name, Address, Tel, Email. Equipment Rented (Make/Model), Condition. Payment Terms (Number of payments - typically 24 months, monthly rental cost, method of payment etc). I also want to be able to calculate income by week/calander month.

I am happy to take any additional questions.