Right now I begin from zero. Im looking to build a website like Icegold ([url removed, login to view]), but it would be different, you can choose two systems, one like Icegold not need to register, the other part is required register to use some services, customizable any time.
Build database on MySQL to storage client info, fees, rates ...
Applied SSL + cURL to operate secure payment.
Applied MCrypt for strong encryption of sensitive data.
More things like required confirmation turing number/word to access your account or batch opperation.
Basically I will work with e-gold currency (sell/buy) using moneygram, westernunion, paypal, wire transfer ... Open functions to add other e-currencies in the future.