How durable is the insulation on magnet wire?
It all depends on what insulation is used.  There are lots of different kinds of insulation and manufacturers make them with different thicknesses (single build, double build, triple build, etc.).  Most data sheets show the results of an scrape abrasion test.  In this test, a sample of the magnet wire is secured firmly in place and a needle is scraped along the surface of the magnet wire.  The datasheet usually records the number of scrapes the insulation can withstand until the needle breaks through the insulation and shorts the wire.  

So that spec on the data sheets will give you a good relative feel for how different magnet wire types compare to each other.  But it doesn't really answer your question of how well magnet wire will work for what you are doing.  Here are a couple of thoughts.  I think you'd be surprised how tough a good quality magnet wire can be.  A popular type in the motor industry is a heavy build MW-35.  It holds up pretty well and should be able to withstand being assembled.  Just try not to use any sharp/pointed tools that could scrape or puncture the insulation.  Also keep in mind that for many, many magnet wire applications like motors and transformers, the magnet wire gets coated with a varnish or epoxy to give it more long term protection against rubbing, vibration, etc.  That doesn't mean your application would need varnish but magnet wire is very often used that way.

I think if you pick a good quality magnet wire and are careful not to nick or scrape it during assembly, you should be okay.