Planning out a system

I am a computer tech. I have a decent linux background.

I have not decided on whether to run Asterisk Now or simply install Ubuntu and install Asterisk. I am leaning towards Asterisk Now because the LiveCD looks interesting and easy to set up.

I have a client that has an office 4 miles from the nearest ANYTHING. They have no power, no water, certainly no phone service. They have a 10kw generator that runs 24-7 that provides power.

My idea is to run a 5.8ghz wireless ethernet bridge (around 3 megabits per second full duplex, 6 megs half duplex) to the site.

They only need one phone number but would like to accept 4-6 incoming calls at once, and have the option to make 4-6 outgoing calls as well.

I am thinking I will need to get with a SIP provider and order a SIP trunk. Then I simply get 6 SIP ip phones. I then build a linux box with two network cards, plug one into the internet, plug the other into the lan. With a public IP address I should then be able to configure the software PBX functions of the AsteriskNow box. I then configure the AsteriskNow box to work with the SIP phones on the LAN. Configure the DID functions, setup extensions et cetera. At that point, they should be able to receive and make calls on the IP phones, correct?

Does AsteriskNow provide remote voicemail recovery et cetera? I previously setup a Fonality box with with SIP trunks but it was fairly expensive even for SIP. Does the Asterisk box support similar functions?

Also, how much bandwidth will a AsteriskNow box use with 4-6 phone lines? Most of the traffic will be incoming, thereby utilizing mostly download bandwidth. Will an 800kbps cable modem be fast enough to make reliable communications? I could always go the T1 route, and I know about dedicated bandwidth et cetera I am just curious what kind of bandwidth saturation to expect.

What about on the client side? What kind of lan throughput can I expect the VOIP system to eat up?

Thank you in advance for your help.