asterisk & a2billing customization

i have very little capital to start a project for me to earn some money .. and because i have good general experience in VOIP and Web applications i want a project i can manage with a small stuff ... as i saw the market at my aria , it is better for me to start International VOIP Calling service. here is the details for what i need ( based on asterisk and A2Billing ) : 1 - i will have several multi-channel SIP Trunks from a wholesale provider (mostly from [login to view URL] ). 2 - online simple login/register form for the users which they can pay and recharge using paypal and check their balance and CDR . 3 - the accounts must be IAX with the possibility to change the IAX port from the server(sure for all the accounts ) to avoid the blocking. 4 - callback service using callerID ( CID will be checked , if it is for one registered customer it will call him back and play IVR telling him the available balance and then asking him to dial the destination number ) 5 - possibility to generate Prepayed cards and sure custom Minute based rates for each country based on the international prefix. 6 - the activation of the prepayed cards and the confirmation of the online registered accounts will be through SMS 6 - the other things to make the project completed and ready to lunch ( except the graphic & multimedia designing ) those are the headlines ... remove everything from the a2billing which we dont need so the management will be easier.