This is possible and can be acheived by several method.
- First JMS propose a full system that allow create website from the front-end.
You can also call you specific script from JMS when creating the website from the front-end.
It is also possible to execute special Plugin to do special task.
We have developed one that create a bridge to VirtueMart in aim to let VirtueMart manage the ordering and the payment.
You could also develop you specific interface and call JMS low level function to create the website.
For example we have recently develop for a customer a "batch website generation" to allow create automatically 1000 dealers websites based on an existing one.
We are ready to develop specific things and also provide specific support if required.
You can find our price support in the Joomla Extensions menu.
www.jms2win.com/download?page=shop.browse&category_id=1
JMS propose also the possibility to give a validity duration for the creation of website.
Most of you request is possible in standard with JMS.
If you want to have your own interface, you could develop a specific component or template to revamp the JMS look.
I suggest you have a look to the video present in the tutorial step 13 that present the creation of website from the front-end.
www.jms2win.com/tutorial