I've done a week in France fixed and few short w/e trips.
Defiantly recommend a rear brake. I only had a very poor front brake when I went to France. I was carrying quite a bit of stuff because I was taking some of my girlfriends stuff and all but this most gentile leg braking is very difficult, I felt my knee go once and was lucky it was at the end of a day and only a slight pull. This is coming from someone who has run brakeless around town in the past so I am perfectly competent with fixed braking techniques. Subsequent w/e overnight tours had a rear brake and has made life do much easier.
I personally run 74" / 65" but have never been loaded anywhere hilly only on unloaded day rides. I'm a relatively strong
climber though, you know what your capable of. I would prob drop to some thin like 69" / high 50's ish if I was going somewhere with long hills, maybe even a freewheel if I was going down some really long downhills, short steep hills can be powered up or walked and it makes little difference. You could always carry one spare cog. Checkout this tool for a good all in one fixed gear multi tool by pedro.
http://www.velosolo.co.uk/shoptool.html
I also like to run a 28 mm tyre on the back for a little extra protection of me and the rim when loaded.
Check this link
http://fixing.letourdeoz.com/ for a dude who went around oz.
Another link for you
http://www.greywoolknickers.net/BikeTrip07/index.html
Are you taking all of your food from home for the entire trip? Your food list is very specific.