Welcome on board; you will find here a great community in the true FreeBSD spirit, with some (many) extremely talented people (me excluded, as I have claimed myself the title of eternal noob on this forum) ;D
People are nice over here, and always willing to help out. What often helps of course is if you provide clear questions, and clear information as to what you've done yourself, what errors you've seen, etcetera. I think I sort of missed your question to begin with; what is it you need help with? Can you formulate concrete, detailed, questions?
As a suggestion: given church, I would setup a VLAN for your guests, and put some content filtering on it (Squid + Squidguard, or Dansguardian). So keep LAN for trusted computers, and VLAN for guests. Captive Portal seems typical for this setup too.
On the firewall level, I would absolutely add BB's pfBlockerNG, a package you can't do without. Snort, or Suricata, comes to mind too of course (layered defense: pfBlockerNG blocks bad IP's based on reputation lists, Snort/Suricata examine content of packages and block when something bad is found).
Depending on how many guests you will have on your network you will probably also like some traffic shaping, but although I have that in my setup, I have a limited number of clients in my networks which makes it easy to configure. You probably have many, and I am not sure how you could set this up efficiently, so perhaps people more knowledgeable in this area (remember, eternal noob is my © on this forum ;D ) can help you there.