Using a higher voltage rated capacitor is perfectly OK, but need to be rated for the voltage you are working on with allowance for surge margins etc.
You need to tune a RPC, see the post by Fitch Williams here.
www.metalworking.com - /dropbox/_1998_retired_files/
Look for the FRW files.
N.A. residential supply is now generally 120/240, the old standard was 110/220.
The origin is a 240v centre tapped single phase transformer, the phase difference is still 180 whether 120 or 240, hence single phase.
Even if you were to use 2 phases of a 3 phase supply it would be termed single phase if there is no other reference involved, i.e. neutral etc. As the phase difference would still be 180.
The phase angle difference of 3 phase is 120 deg, but this is referenced from a 0 or neutral point.
The Run capacitors Must be AC continuous rated, only the start cap. can be intermediate rated, due to the large value, a continuous rated start cap. would be quite expensive.