Changing from a triple to a double is a bit more involved that just changing the crank, there a the shifters and front mech to think about, these may or may not be an issue..

For the Bottom Bracket, the spindle length you currently have probably won't work, as triples require a longer spindle than doubles, so staying with your current BB will give you a too wide chain line.

For thread TPI, if you currently have a UN40, this will be an English thread, and either 68 or 73mm width.

Would be useful if you post up what your intended crank will be, as this will be helpful for advise on what BB you will need.