Software

There are a TON of tips and tricks on http://www.msexchange.org for Exchange related tasks. We currently have our Exchange server completely hidden behind the firewall. The firewall forwards the SMTP traffic internally.

You should start looking around the internet for white papers on Exchange deployment. Your questions are very basic and can be answered any of a number of different websites.

1. If at all possible, use an ISA server to publish your Exchange server to the Internet. When properly configured, it is the most secure way to use Exchange from outside your organization. Read up on ISA at http://www.isaserver.org. They have MANY tutorials on how to effectively securely publish Exchange.
2. Since you only have 30 users, have you looked at SBS 2003 R2? It will make your job MUCH easier as a network admin. If you go this route, get a membership to http://www.smallbizserver.net for great information on how to properly set up SBS.
3. I would highly recommend that you use a split DNS setup and install your AD environment to something like ad.company.com where company.com is your external DNS. Read more about this here. http://tinyurl.com/aadwq

Now, if any of this seems above your head, hire a consultant for help designing your network. You can still do the work, but get some help answering your questions up front. Good luck.

I would highly suggest going to Microsoft's site and reading up on their white papers for Exchange Deployments. They have case studies and other tips that would definitely help. I also agree about contacting someone who might have a little more understanding of setting up the network. Your questions are good ones but you are making it harder on yourself then it needs to be. If you already have a firewall there is no need to get a public IP address for your Exchange Server as the firewall can route the traffic. You would need to set up an MX record for DNS with your current ISP, who I would take it is currently handling your public DNS records. If that is the case they could probably even help you set up the rule or offer suggestions for configuring your firewall. Otherwise go to your firewall provider and get assistance from them they definitely should be able to assist in that area. Again good luck and check out Microsoft's site. It is their product they should know how to set it up properly.

i have been looking all over for a clear explanation on setting up this server and adding users to it, then being able to confirm that it works. can anyone help me out? this is a little overwhelming for me.