Khanivore: Definitely start getting used to it now. Really important to find out where the pack might rub, and therefore where you need to apply glide stick or whatever before the ultra, not on the day!
Andy, if you're still in that much pain something is wrong with the diagnosis and/or the treatment. You need further assessment.
As another data point: I nursed a tender PTT through five 50-mile trail races last year; it was improving when I came off my bicycle and tore it. Six months off, five months of those wearing a PTT ankle brace whenever I was weight bearing (even in the shower). Ultrasound about four weeks in showed the tendon was a mess, including a tear. MRI at six months showed a tear and degeneration (but it had been in a brace and unused for five months - of course it had degenerated!).
I've spent the last six-seven months gradually returning to running. Now managing e.g. five-mile cross-country races and the longest distance I done so far is about 14 miles. I'm wearing minimalist shoes (VivoBarefoot and Inov8 zero drop trail shoes) with half-length off-the-shelf Scholl Orthoheel orthotics to give the arch a bit of support. Hoping to get back to shorter-length (c.30 mile) ultras during 2015 and 50-milers in 2016, but presently NOT entering for any long races so as not to put ptessure on myself to do too much too soon.
What you'll need to wear to avoid feeling really cold will vary hugely between people. It also depends how fast you're running. If you're on a long steady run of 20 miles on a day when it's windy, raining and cold, you might want a hat, gloves, long-sleeved base layer (or short-sleeved plus arm warmers) and a lightweight breathable waterproof jacket as well. There have been sub-zero days with a biting wind when I've been very pleased to have full length tights with a windproof panel over the front of the thighs.
And then there people who seem to be fine in shorts and a T-shirt even on the coldest days.