45 degree blades are universal and are what we ship with all our cutters.  60 degree blades are slightly longer and therefore can be good for cutting thicker material such as reflective vinyl or sandblast mask.  There is no good measure for how long your blades will last.  Everyone cuts different amounts and types of materials, as well frequency.  Your blade could last 1 month or 5 years.  You will know your blade is dull when you go to weed vinyl and start noticing that parts of your job will not be cut all the way through the vinyl to the backing paper.