Airport network & ADSL modem with Mac OS X Server config

Let me try to answer some of your questions ...

I am under the impression that to access the MBP server from the internet, I'll have to deal with port mapping.

That would be correct if you plan on accessing any of this server's services from the Internet.

but maybe I can get around this headache (i.e. not have to deal with port mapping at all) by using a modem or modem-router in bridge mode, and using an Airport Express, Extreme, or TimeCapsule?

Q2--Is that actually true?

Yes, the typical configuration would either be a modem and router or a combination modem/router for Internet access ... and no. Any router between the Internet and your server will have to be configured for port mapping in order to access it from the Internet.

I'm not opposed to mapping, but I may or may not be able to get a static IP address on my new connection.

I am assuming that the static IP address that you are referring to is on the public or WAN-side of your router ... correct? Regardless, port mapping and getting a static IP address are not directly related to each other. Most ISPs will provide you with a dynamic WAN-side IP address. In this case you would assign a LAN-side static IP address to your server.

Q3--Does the Airport Express offer the same capability for Back to My Mac / network access to a server machine as Airport Extreme or Time Capsule? (I don’t even know if Back to My Mac is even applicable in the server context.

There are basically two "flavors" of BtMM: One for the AirPort base stations and the other for a Mac computer. The former will allow you to access the base station and any attached hard drive. The latter allows direct access to the Mac computer.

If I set up a basic modem or modem-router in bridge mode and connect it to an Airport Express, I guess I would connect it via LAN. Is gigabit LAN important in this case do you think? Or will the Express' 10/100base-t be plenty? I know it's subjective, but...

Where Gigabit Ethernet pays off is both on the WAN & LAN side of your network. You may not have Gigabit Internet bandwidth just yet, but it won't hurt to have it available for future growth. On the LAN side, you will want all of your Ethernet connections to be Gigabit if given a choice to provide you with the best overall bandwidth for things like transferring files or streaming.

Do you think it’s a bad idea to go with an Express for this purpose — is the lack of gigabit ethernet a bad investment? I love AirPlay on Airport Express, I have used it lots over the years, but maybe now with a server I can deliver music from server to audio system in a better way, and I should really be considering only Airport Extreme or Time Capsule for their gigabit ethernet and wifi range? And other features?

Not necessarily, but if your budget can afford it, why not get both an Extreme or Time Capsule AND an Express so you can do both well.

Q5--And if gigabit is deemed essential, then should I only be considering modems with gigabit ethernet?

Yes.

Q6--What considerations should I be taking into account when considering modems and routers for this storage? I think I will set it up with one of my existing external FW800 drives connected to my MBP server.

Basically that they have Gigabit Ethernet interfaces and for the Wi-Fi side support 802.11n. Support for 802.11ac, at this point in time, is not critical.

Q7-- What about using an Airport Extreme with an external HDD connected, or Time Capsule, as my network storage solution?

The issue will be that the USB connection will be the "bottleneck" of your overall data path. Both from the local network and from the Internet.

Could I set it up so it was accessible from the internet when I'm away?

Potentially, yes.

Q8--I also need network printing, and my printer is not wifi enabled. I would either connect it to the MBP server or to the Apple router I guess. It would be very useful to be able to print from iOS 7 devices as well, though my printer itself is not AirPrint capable.

To print from iOS devices when the printer is not AirPrint-ready, would require a third-party solution, like Printopia that would run on your Mac.