To accept multiple incoming calls in parallel you need either multiple individual lines from your service provider or a 'trunk' connection (either traditional digital trunk or an IP based SIP trunk).
There are quite a few good detailed Asterix IVR guides - some links from an answer to a similar question are:
- http://www.asterisk.org/get-started/applications/ivr
- http://www.freepbx.org/support/documentation/administration-guide/creating-an-ivr
- setup an IVR with Asterisk
On the hardware side, it depends what connection you end up getting from your service provider, but you will need some sort of line card to terminate the telephony if it is traditional analogue or digital. See this Asterix page for more information:
Note that your service provider (or an alternative provider in your area) may be able to provide you SIP / IP based 'trunks' in which case you would not need this extra hardware. It might be worth checking this out depending on your specific requirements and the price etc.