Asterisk Expert for previous requirements system

I have planned to change my old PBX to a new Asterisk PBX. What I need is a PBX that supports 12 internal lines with VoIP phones, I need to make internal calls and configure wich internal phone can make call outside. I have 12 voice mobile lines and 2 data (for faxing) mobile lines. These are what Vodafone says "fijo en el móvil" I have one phone number for receving calls the other ones are used for transfer the calls and let free the number for more incoming calls. What I need from Asterisk PBX is: - When an incoming call comes transfer the call to other line and then transfer it to the desired internal phone. - Configure a welcome message and when we are out of office hours a message on our opening hours. - When all lines are occupied,set a "please wait" message. Before to start this project we need an Asterisk expert that explain me if that would be posible with Asterisk and Which are the system requirements to make this project work like a charm? Before we meet the system requirements we decide to implement or not the Asterisk PBX We need a list of CPU, RAM memory, Hard disk (SATA or SAS), Ethernet devices, PCI cards to support the mobile lines (SIMs), Switches and VoIP phones. Also we need that the Asterisk expert tells us how much money his work will cost. I mean a bid to make this project work after we buy the required hardware.