Ti spokes will stand the test of time, they will lay there in the box forever.
They are very springy, it is not so much that they stretch after building but they just don't ever quit being springy and come up to good tension.
You CAN NOT use alloy nipples with Ti spokes. Sometimes they will seize as thread them on with your fingers. Ti and aluminum do not get along. If you use brass nipples you lose most of the weight benefit of Ti and the best place to save weight on a wheel is at its outer edge, rotating mass and all that.
You need to use Ti prep if you build with Ti spokes so something like spoke freeze or spoke prep does not work very well.