davedickson: Apologies for the late reply, yes I think 1TB should be plentiful to cover maemo/meego related repositories, including all the firmwares and what not such as:
- Developer environments (scratchbox)
- All the minor projects that has either been completed and/or is incomplete (and abandoned or ongoing) such as cordia, Mer and what not.

There's a few more other things that may need to be covered such as:
- maemo/meego wiki pages (unless X-Fade is willing to negotiate it'll be hard to mirror them without hogging excessive space).
- t.m.o. threads (talk.maemo.org), there's lots of useful information that has not yet been `wikified'.
- m.x.r. (maemo cross-reference site), very handy for any interested developers. Again, most of the site is dynamically generated and without negotiating to whomever owns it to mirror it properly will hog excessive space if one tries to wget it).
- bug site, handy to know what was fixed, etc.
- garage site: home of many 3rd party developers' apps. Again very handy and may include things that were not added into the main repositories due to various reasons.
- Qt stuff, needless to say that its used extensively on fremantle.

Hopefully that should cover everything that's related to maemo and its rather extensive history of things. All in all I really do not have a clue on how much will the final size be for everything aforemented here.

misterc: Dynamic IP address can be easily addressed with Dynamic DNS providers. They are mostly free/cheap and is generally fuss free.

Last but not least, two more things worth noting:
1) archive.org can be a really handy place for maemo.org's final resting place should the various alternative mirrors decides to move on. Better yet would be to try and somehow negotiate with them on making their lives a little easier by not mirroring maemo.org site constantly and instead of keeping all the chronological mirrors of maemo.org is to have one big mirrored version from whomever decides to pull the plug on their mirrored hosting.
2) It would also be somewhat a wise idea to have maybe a torrent and/or rsync server set up on alternative mirrors so that any other potential mirror can keep up to date with the alternative mirror (to keep it in sync in other words).