General Questions

I'm about to get the opportunity to get real fiber 100Mb, and then it will be a big switch in the basement, providing all the apartments with 100Mb (or 50 or whatever), and IP-phone and everything.

But, I guess it will be like a regular LAN, and static IP and stuff, the whole building as a big LAN, and I wonder if I can still use my M0n0wall router as a firewall, just plug what comes in here into the WAN port and continue to use it as before?

I can see in WAN you can only choose "static", "dhcp" as I have now, "PPPoE" and "PPTP".
Is it likely none of them will match?

Thanks
Would like to know if I should order that or not, dont want to skip my external firewall, and dont want to miss the VLAN-trunking and everything that little box handles

If you're getting Fiber access, you'll need a Fibre card that's supported by the operating system.  If you're lucky, your ISP will provide a CPE that gives you a Copper Ethernet interface to use.
Not to mention, the CPE will then secure the rest of the external network by performing the appropriate authentication on the fibre uplink (they won't want you hijacking other IP addresses).

You're likely to be provided with a Static IP or DHCP connection so use the appropriate setting in Monowall.  Best that you actually ask what you're provided with before signing up for the service.