You can get either the 110mm or 120mm skins, and trim them to fit to your needs. As for shipping, add it to your cart, and put in your postal code/ZIP and it will tell you shipping to Australia and costs.

You should get skins to just about 0-10mm NARROWER than the tip width of your ski. THat way when you trim them they are edge to edge fit providing the best performance. Length can be done to fit easily as well.

You trim them to fit, so i think that would cover almost any length out there except for old school DH boards.

This skin will work fine. I would say get a 120mm, then you have less to trim on the tip, but it is more important for you to be wall to wall with skins in the middle of the ski. The black diamond STS glidelites are also a great skin that would work well with a twin tip.

They are all pretty good, I've personally had experience with Black Diamond and I like them a lot. The Ascension's are a stiffer more burly skin and the Glidlite's are a lighter weight somewhat thinner skin. Both are great just depends on how much you are going to uses them and what you are looking for.

The skins are a uniform width throughout, so you would purchase a skin that is a little bit smaller than the widest part of your ski.

best option are skin savers - basically a nylon mesh half the length of the skin. You fold the skin in half with the mesh in between - they still stick together and are easy to pack away but are also easier to pull apart again and it supposedly saves the adhesive

By "short term storage," I assume you mean something like in the car on the way to the trailhead, and in your jacket or pack on the descent. For those situations, I fold and join each skin individually, in half, glue side to glue side. Joining two full-length skins together cleanly is very tricky, especially if it's windy or snow is blowing around. It's usually not worth the effort.

They all glide pretty similarly, but you may want to aim your search towards the Black Diamond Glidelites.